AP_HAL: add force_safety_on method
HAL_PX4: implement force_safety_on
HAL_VRBrain: implement force_safety_on
AC_WPNav: WP_SPEED_DN parameter range to 0~500

Previous permissible descent speed of 10m/s was unnecessarily lenient.
Users can still bypass the suggested range through the MP's full
parameter list if they really want a very high descent speed.
Frame_params: 3DR_Aero_RTF.param Changed tuning
Frame_params: added 3DR_AERO_M.param
Copter: reset battery_fs after dis/rearming
Copter: define limit for baro vs inav alt disparity
Copter: typo fix for baro vs inav alt disparity definition