- new modules/simulation directory to collect all simulators and related modules
- new Tools/simulation directory to collect and organize scattered simulation submodules, scripts, etc
- simulation module renamed to simulator_mavlink
- sih renamed to simulator_sih (not a great name, but I wanted to be clear it was a simulator)
- ignition_simulator renamed to simulator_ignition_bridge
- large sitl_target.cmake split by simulation option and in some cases pushed to appropriate modules
- sitl targets broken down to what's actually available (eg jmavsim only has 1 model and 1 world)
- new Gazebo consistently referred to as Ignition for now (probably the least confusing thing until we fully drop Gazebo classic support someday)
- always check with state machine before reboot/shutdown
- respect BOARD_HAS_POWER_CONTROL (shutdown from command, low battery, power button)
- px4_shutdown_request add optional delay and always execute from HPWORK
- px4_shutdown_request split out px4_reboot_request
- this is one of the last pieces of the system that still depend on DriverFramework
- add new SIM_GPS_NOISE_X parameter for optionally increasing the GPS noise multiplier (was previously a gpssim command line option)
- add SIM_x_BLOCK parameters to block sensor publication
- SIM_GPS_BLOCK
- SIM_ACCEL_BLOCK
- SIM_GYRO_BLOCK
- SIM_MAG_BLOCK
- SIM_BARO_BLOCK
- SIM_DPRES_BLOCK