Copter: sanity check throttle deadzone
InertialSensor: reorder .cpp file to match .h

No functional changes
INS: add get_accel_health_all and get_gyro_health_all

Returns true only if all available accels or gyros are healthy
Copter: check all gyros and accels in pre-arm check
Copter: individual accel and gyro status to GCS
VRBRAIN: modified target clean
DataFlash: Added four more channels for logging
Copter: enable mount control with channels > 8 for radios with SBUS.
AP_Compass: VRBRAIN. Deal with external mag connected on internal I2C on VRBRAIN 4.5
This enables user to set the external parameter to true even if only one compass is connected