Migrate a few more var initializations from the Mavlink class constructor list to the respective declarations.

Whitespace formatting in mavlink_main.cpp/h and begin work of some variable initialization at declaration in mavlink_main.h.

Delete unnecessary #includes from mavlink_main.cpp and relocate a few #defines to mavlink_main.h for future variable initialization work.

The effect was that threads that tried to exit were unnecessarily kept
running.
This did not cause problems except for increased resource usage.

This solves a potential dead-lock when trying to shutdown: a call to exit()
stops all threads and calls all destructors for static objects.
The destructor of LockstepScheduler takes a lock. However this is not
safe, as the lock could already be taken (by any thread).

Add const specifier to remaining methods utilizing mavlink_message_t and similar message pointer types.

Cut case MAVLINK_MSG_ID_VISION_POSITION_ESTIMATE content and paste into handle_message_vision_position_estimate() method. Add const specifier to publish_odometry_topic() method.

- jMAVSim in PX4/Firmware (a97151fe): https://github.com/PX4/jMAVSim/commit/0c25b7c18990a64fc851cfd7fe3aac9a4060aea3
    - jMAVSim current upstream: https://github.com/PX4/jMAVSim/commit/8b2f4568e05935af57782fd0db9a434f733cc800
    - Changes: https://github.com/PX4/jMAVSim/compare/0c25b7c18990a64fc851cfd7fe3aac9a4060aea3...8b2f4568e05935af57782fd0db9a434f733cc800

    8b2f456 2019-02-28 Julian Oes - Merge pull request #95 from PX4/shell-style
3d0174a 2019-02-27 Matthias Grob - Fix shell script style

    -  mavlink v2.0 in PX4/Firmware (1a2b88ea30ae3bec38d2e9f11793042d7582506a): https://github.com/mavlink/c_library_v2/commit/f073569b746b6533c1715b0bbfed6c988444b257
    - mavlink v2.0 current upstream: https://github.com/mavlink/c_library_v2/commit/2a47f11e73eef6d817af7934692b1223d7fb434f
    - Changes: https://github.com/mavlink/c_library_v2/compare/f073569b746b6533c1715b0bbfed6c988444b257...2a47f11e73eef6d817af7934692b1223d7fb434f

    2a47f11 2019-03-01 PX4BuildBot - autogenerated headers for rev https://github.com/mavlink/mavlink/tree/747c3e73e9ad28e8011cdc5c98faf56752b1d32a

Refactor set_publish() logic so that a default false value is not (re)set each loop in simulator_mapvlink.cpp and provide a default argument to set_publish() in simulator.h.

Create Simulator::set_publish() method and Simulator::_publish member variable to allow redefinition of the Simulator::handle_message() prototype to match MavlinkReceiver::handle_message().

 - fixes #11317

The simulator had hardcoded component ID and system ID (sysID was 0), ignoring what was set up in the params MAV_SYS_ID and MAV_COMP_ID. This caused an issue with multi-vehicle simulations that that rely on sysID to identify the vehicles.

Signed-off-by: Gabriel Moreno <gabrielm@cs.cmu.edu>

In CONTRIBUTING.md, the current link to the coding style leads to a
404 error. I've replaced it with a link to the Source Code Management
part of the developer documentation, which is where the style guide
seems to be now.

This reverts commit 0df34af1.

   The cause of the stack detection fault is because of the
   level of nesting in the start up script. We need to
   determine the worst case configuration and set the
   bar there.

   This fault occurred some 42 calls deep due to script
   calling script (repeat).

   The HW stack check requires as a margin of 204 bytes. That is
   ISR HW stacking of CPU(8) FPU(18) registers and SW stacking of
   CPU(11) and FPU(16) registers. Total CPU(19) registers is
   68 bytes and the total FPU(34) registers is 136 bytes.  On
   a system with a separate ISR stack This only needs to be 104
   so there is 100 bytes of headroom. But as coded the detection
   will give a false positive detection and fault. This does not
   mean that the stack will be corrupted.

   Adjustments to that stack can have no effect due to rounding.
   A stack size of 2608 and 2616 can yield the exact same size stack.
   So even when the failure is due to a 4 byte overflow, it can take
   greater than a 16 bytes increase to fix it. Because the final
   stack size is calculated with an 8 byte alignment after a 4 byte
   decrease. So 2624 becomes 2620 at runtime and will boot
   with SYS_AUTOSTART=4001.

 - support range based for loops
 - add remove() method to remove a node
 - add clear() to empty entire list and delete nodes
 - add empty() helper