This adds the env variable PX4_SIM_SPEED_FACTOR to set the speed factor
to run SITL at.

Without setting the device_id, the preflight checks fail because the
calibration is not found.

This switches from UDP to TCP to connect to jMAVSim.

This adds the option to connect over UDP or TCP for mavlink to the
SITL simulator.

Also, this includes a bunch of general cleanup and refactoring of the
simulator interface code. For instance sending of mavlink messages was
put into separate functions and unneccessary comments were removed.

Also, this now sets the timestamp sent by the SITL simulator in the
HIL_SENSOR message in order to enable lockstep.

When we poll on vehicle_local_position we shouldn't do yet another
orb_check but copy it first up.

These functions won't be used any longer with the new implementation.

This fixes a race/lockup happening in the DriverFramework scheduler.

We shouldn't be using module here.

This is required so that the SITL simulator receives a feedback from
PX4.

This uses the "fake" px4_sem based on mutex and condition_variable on
all POSIX system, not just macOS and Cygwin. This means that we can
change px4_sem_timedwait under the hood and inject the simulated time.

This integrates the lockstep_scheduler, so that the system time is set
by the mavlink HIL_SENSOR message.

This means that the speed factor is removed and the speed is entirely
given by the simulator.

This should be enough for now, especially when we want to raise the
speed of the simulation.

This is just an intermediate step until we can copy the sources over.

These contains some rough changes trying to get SITL to speed up by a
SPEED_FACTOR.

This platform time code probably requires some more thought and refactor
but this gets a demo at 4x working.

This adds the argument -f for a speed factor to speed up the simulation.

This is another step to isolate time from the system.

This is a step towards isolating time from the system.

    - v2.0 in PX4/Firmware (3256e67fdc5e86b5d8c6378ea24ff8a065b65ba8): https://github.com/mavlink/c_library_v2/commit/c38176a0a63556815ea117c6877ce2dd18739231
    - v2.0 current upstream: https://github.com/mavlink/c_library_v2/commit/175ab6725cc0d96827d04ffeeaf3a7797a9abdbf
    - Changes: https://github.com/mavlink/c_library_v2/compare/c38176a0a63556815ea117c6877ce2dd18739231...175ab6725cc0d96827d04ffeeaf3a7797a9abdbf

    175ab67 2018-12-17 PX4BuildBot - autogenerated headers for rev https://github.com/mavlink/mavlink/tree/eaa914c7d9789bc37c9a6a59a5bd1171634bd429
4d5fa0d 2018-12-14 PX4BuildBot - autogenerated headers for rev https://github.com/mavlink/mavlink/tree/48df7ea08abb5d87df6ccb1f9a69b91ff3b89c7a
b65cfcd 2018-12-14 PX4BuildBot - autogenerated headers for rev https://github.com/mavlink/mavlink/tree/b671d3c24d5fc6aa964cd07a4a46566d4dbd7862
8473fe2 2018-12-13 PX4BuildBot - autogenerated headers for rev https://github.com/mavlink/mavlink/tree/2b9d470011a0d62fbfc3183ee172201e5170f7af
5a186d4 2018-12-13 PX4BuildBot - autogenerated headers for rev https://github.com/mavlink/mavlink/tree/68ed09da2e341b2932d9c9d761d7baa811191dc2

    - matrix in PX4/Firmware (3e5d66580520e5ae64555c5fc9252c6c661389e3): https://github.com/PX4/Matrix/commit/9c0acfba36a928b7b002eea3a9dca54a5a0c1250
    - matrix current upstream: https://github.com/PX4/Matrix/commit/18fba8221cc1840964c43f04d8c2aa21857e1b9b
    - Changes: https://github.com/PX4/Matrix/compare/9c0acfba36a928b7b002eea3a9dca54a5a0c1250...18fba8221cc1840964c43f04d8c2aa21857e1b9b

    18fba82 2018-12-16 Matthias Grob - quaternion: improve comments
a4f39c0 2018-12-16 Matthias Grob - quaternion: reuse existing dot product

* the bearing difference between the waypoints and aircraft to landing point should be wrap_pi'ed