Previously the rate controller disabled updating the integral below 20%
throttle. This is not ideal for several reasons:
- some racers already hover with 20% throttle.
- for acro it is important to always keep the integral enabled, it has a
  noticeable effect on flight performance.

It's now the same way as in the ARM logic further down.

A reason for using switch arming in the first place is that you cannot
accidentally disarm in-air with the sticks during acrobatic flights.

It also adds a low-throttle arming requirement for switch arming.

This changes the arming logic such that the preflight checks don't need
to be satisfied if arming happens < 5 seconds after the last disarming.
This allows to recover from accidental in-air disarming.

if fRunPreArmChecks was set to false, there were still cases where the
preflight checks could be called. This fixes that.

arming_state_transition() with fRunPreArmChecks=false is only called
when entering & leaving preflight calibration mode.
All other places use fRunPreArmChecks=true, which means there is no change
for these.

- this matches the logic in arming_state_transition()
- if Commander::preflight_check was run in armed state and the checks
  failed, disarming was not possible anymore
  (because disarming checks for condition_system_sensors_initialized).
  That is currently not the case, but the existing logic is way too fragile.

Alternative solution: check if armed in Preflight::preflightCheck, and
only transition to false if disarmed (but also respect the re-arming
grace period).

- libuavcan in PX4/Firmware (fab974fde713b9de0ece1b85239d9dc52622052e): https://github.com/UAVCAN/libuavcan/commit/231b221b64265db4e98f86e53721316f9e17e143
    - libuavcan current upstream: https://github.com/UAVCAN/libuavcan/commit/dfcdf22eda16ff06847976fd6c7f40671fc92eb5
    - Changes: https://github.com/UAVCAN/libuavcan/compare/231b221b64265db4e98f86e53721316f9e17e143...dfcdf22eda16ff06847976fd6c7f40671fc92eb5

    dfcdf22 2018-06-26 Pavel Kirienko - Merge pull request #142 from thirtytwobits/feature/issue141
529a376 2018-06-21 Dixon, Scott - Issue #141 Add Vagrantfile to automate dev environment

    - nuttx in PX4/Firmware (537fe886015be0ccb6b691a8a2802fb29d17c410): https://github.com/PX4-NuttX/nuttx/commit/63775322bf25adb406594f8e610122fe0cef2f7a
    - nuttx current upstream: https://github.com/PX4-NuttX/nuttx/commit/f57752b6f16f54bd50188024475657c6a7a1604c
    - Changes: https://github.com/PX4-NuttX/nuttx/compare/63775322bf25adb406594f8e610122fe0cef2f7a...f57752b6f16f54bd50188024475657c6a7a1604c

    f57752b 2018-06-25 Daniel Agar - Merged in dagar/nuttx/pr-fixCompileError (pull request #660)

Displays all enabled streams and their configured rates.
Example output:
instance #1:
        Name                Rate Config (current) [Hz] Message Size (if active) [B]
        HEARTBEAT                       1.00 (1.000)    21
        STATUSTEXT                     20.00 (6.320)
        COMMAND_LONG                  unlimited
        ALTITUDE                        1.00 (0.316)
        ATTITUDE                       25.00 (7.900)    40
        ATTITUDE_TARGET                10.00 (3.160)    49
        ESTIMATOR_STATUS                1.00 (0.316)    44
        EXTENDED_SYS_STATE              1.00 (0.316)    14
        GLOBAL_POSITION_INT            10.00 (3.160)    40
        GPS_RAW_INT                     1.00 (0.316)    62
        HOME_POSITION                   0.50 (0.158)
        RC_CHANNELS                     5.00 (1.580)
        SERVO_OUTPUT_RAW_0              1.00 (0.316)    49
        SYS_STATUS                      5.00 (1.580)    43
        SYSTEM_TIME                     1.00 (0.316)    24
        VFR_HUD                        25.00 (7.900)    32
        WIND_COV                        2.00 (0.632)

This implementation does not need more resources.
It's not super efficient in terms of runtime, but it's also not something
that is called often.

- add datarate
- add UDP remote port
- add partner IP

Plus correct return value.
Iridium links are below that.

    - sitl_gazebo in PX4/Firmware (1dd67e77): https://github.com/PX4/sitl_gazebo/commit/b5a92095bfb1b6a218a80f58ad9fe09c89ef4598
    - sitl_gazebo current upstream: https://github.com/PX4/sitl_gazebo/commit/3c7d18d0a52657106a3a7190c54006ed6b442071
    - Changes: https://github.com/PX4/sitl_gazebo/compare/b5a92095bfb1b6a218a80f58ad9fe09c89ef4598...3c7d18d0a52657106a3a7190c54006ed6b442071

    3c7d18d 2018-06-19 TSC21 - travis: add -DBUILD_ROS_INTERFACE=ON option to catkin build
e89cf8f 2018-06-17 TSC21 - travis: use catkin build tools
f7a1c4b 2018-06-19 Elia Tarasov - remove unnecessary mavros libs and duplicate CMake message
c495c57 2018-06-19 Elia Tarasov - remove unnecessary dependecies
5c861a5 2018-06-19 Elia Tarasov - remove executable node
7d69268 2018-06-19 Elia Tarasov - remove redundant includes
6ba0eeb 2018-06-19 Elia Tarasov - remove redundant ros packages
9c69a95 2018-06-18 Elia Tarasov - modify target node name and add needed libs
147cb56 2018-06-17 elia - move class member function definitions to implementation file
dc24fcc 2018-06-17 elia - add undefined class varibales

    - v2.0 in PX4/Firmware (5e76f2dca7530404173601b4a231778381d4f3cc): https://github.com/mavlink/c_library_v2/commit/033fa8e7a4a75a0c3f17cea57e3be8966e05f770
    - v2.0 current upstream: https://github.com/mavlink/c_library_v2/commit/f5c0ba684659fbc6c6c5f8777bd30e0b3c32fdef
    - Changes: https://github.com/mavlink/c_library_v2/compare/033fa8e7a4a75a0c3f17cea57e3be8966e05f770...f5c0ba684659fbc6c6c5f8777bd30e0b3c32fdef

    f5c0ba6 2018-06-19 PX4BuildBot - autogenerated headers for rev https://github.com/mavlink/mavlink/tree/40f8149d642892b87c61acf3fb63d2512d06a22a

 LandDetector FW: Fix param min/max values and descriptions as well as some variable names which were wrong/outdated (#9708)

If the PX4FMUv2 board does not have the v5 uploader, it's not possible
to check the silicon revision to make sure it's safe to upload the
firmware which is more than 1 MB. However, if the user is sure the
silicon revision is not affected by this errata, he can upload the
firmware using px4_uploader.py with --force argument. This commit adds
`force-upload` make target to do it more convenient way.

Signed-off-by: Andrei Korigodski <akorigod@gmail.com>

* ecl: Update to version allowing use of flow sensors without gyros

* msg: Update description for optical_flow

Adds advice for publishing gyro rate integral message when no rate gyro is fitted.

Uninitialized `_ping_stats.last_ping_time` caused ping statistics to be printed even when no ping was received.

The uorb subscribe logic got changed for queued topics with
https://github.com/PX4/Firmware/pull/9436, meaning an orb_subscribe will
return past messages as well now.

This lead to an error 'Command denied during calibration' for the previously
received calibration start command.

    - sitl_gazebo in PX4/Firmware (ebc40067): https://github.com/PX4/sitl_gazebo/commit/8a3166bf5d315274cfd503a75880e9837faa9694
    - sitl_gazebo current upstream: https://github.com/PX4/sitl_gazebo/commit/b5a92095bfb1b6a218a80f58ad9fe09c89ef4598
    - Changes: https://github.com/PX4/sitl_gazebo/compare/8a3166bf5d315274cfd503a75880e9837faa9694...b5a92095bfb1b6a218a80f58ad9fe09c89ef4598

    b5a9209 2018-06-10 TSC21 - travis_ci: Add OSX build