simulator in hardware, new module added that allows to run a simulator in the hardware autopilot, for more documentation visit https://github.com/romain-chiap/PX4_SIH_QuadX

 - this extension adds support for Data Structure Description Language (DSDL)

* drivers, magnetometer: added ak09916 driver to support the mag driver emulated by the Here2 gps
* boards: set yaw 270 rotation for external ak09916 driver and only start it for the PH21
* drivers: only start ak09916 when icm20948 is not available on a ph21 setup

This should prevent future regressions when compiling with "Unix
Makefiles" or others instead of ninja as the generator behind cmake.

This fixes build races which happened if "Unix Makefiles" instead of
ninja-build was used as the cmake backend.

For any dependencies of commands on files we need to create a target.
Otherwise, if "Unix Makefiles" are used as the generator the commands
are run in parallel on the different files which often can lead to
races or redundancies in our build.

A nice write-up can be found here:
https://samthursfield.wordpress.com/2015/11/21/
cmake-dependencies-between-targets-and-files-and-custom-commands/#
custom-commands-and-parallel-make

   Addresses #11832 - configure the mixed use GPIO
   that can be the a BLue LED or a Heater as PUSH
   PULL on Cube as to not let the heater input float.

Add back pwm out sim module so HITL simulation works again.

    - ecl in PX4/Firmware (aed3d80d5982f37e8353d6d07e29c79a9260b086): https://github.com/PX4/ecl/commit/f95cd4b3584d029c35b288a39180ddf25b2dd004
    - ecl current upstream: https://github.com/PX4/ecl/commit/c4492b17c1d7bb9b74011efa9890452b091421e8
    - Changes: https://github.com/PX4/ecl/compare/f95cd4b3584d029c35b288a39180ddf25b2dd004...c4492b17c1d7bb9b74011efa9890452b091421e8

    c4492b1 2019-04-09 Martina - do not reset yaw if vehicle on ground
14227ea 2019-04-08 Julian Oes - CMakeLists.txt: fix cmake warning
f97f0b6 2019-03-30 Paul Riseborough - EKF: Remove unnecessary code
43b5e26 2019-03-02 Paul Riseborough - EKF: Fix bug causing continual yaw reset when EKF2_MAG_TYPE = 2

With 24 MHz accesses to the SD card were unreliable. And the chance of
failure recently got worse, so that logging became impossible.

 - needed for code coverage of python scripts

- platform is optional and matters for Visual Studio builds
- `ver` command shows the windows version
and was just my first CI test

    - mavlink v2.0 in PX4/Firmware (88f2a685): https://github.com/mavlink/c_library_v2/commit/171c83700c6318af9ffb4a7ee733567b55a14543
    - mavlink v2.0 current upstream: https://github.com/mavlink/c_library_v2/commit/c6ab0459343c78a6a424514b5f64fa65d8cc0cf8
    - Changes: https://github.com/mavlink/c_library_v2/compare/171c83700c6318af9ffb4a7ee733567b55a14543...c6ab0459343c78a6a424514b5f64fa65d8cc0cf8

This should fix the macOS build.

When using QGC and/or the Dronecode SDK it was possible to get in a
state where the two mavlink instances were both publishing their last
heartbeat_time and cause commander to consistently toggle between
data link lost and regained. With this fix, we only ever look at the
very last heartbeat time and therefore seem to avoid this issue.

This prevents a warning message being printed to SITL users because the
UAVCAN_ENABLE param does not exist.

With this change the param SDLOG_MODE can be used for SITL as well.

loiter mode since it's the failsafe mode

instance protected