Add reboot command for SITL

[unjambonakap]

Solved Problem

Lack of reboot function on SITL
There exists a shutdown that does a rather dirty exit()

Current state of the change

• Functional - can reboot many times, working just fine - no memleaks (for px4_sitl_default)
• debug prints here and there
• temporarily put tracer.hpp that was helpful for debugger resource management issues
• huge change - breakup needed

Solution

A no-hack solution where everything is properly deinited()
It means an unfortunately tentacular in order to achieve the graal: every resource used is then freed()

Non exhaustive list of changes that were necessary:

• reworked the main / Pxh
• Registering modules stop_command/request_stop/is_running in a ModuleManager
• Adding stop functionality on some modules that do not possess it
• Have a replacement LockstepScheduler driver when the SITL module is stopped
• Cleaning of WorkItem removal mechanism. I strongly suspect the existing implementation have race conditions that can be dramatic (to put things in perspective, race happens on module stop())
• Encountered many queue systems. First time really diving in the codebase, platforms/common/include/px4_platform_common/workqueue.h appears almost obsolete (used by camera_capture.cpp. Others?) - It could probably be moved to the WorkItem framework