AP_EPM: EPM cargo gripper library
Copter: integrate EPM library
Copter: EPM enable/disable to APM_Config.h
Copter: Add RSSI_RANGE parameter

Added ability to rescale rssi input voltage. Useful for receivers like
FrSky which have 3.3V output.
Copter: move sensor init from setup(to init_ardupilot

This fixes a bug in which the external led was not being disabled if the
EPM was enabled (they share pins).  The cause of the problem was the EPM
was being initialised before it's parameters had been loaded
Copter: remove reference to COPTER_LEDS
AP_TECS : Reduce tendency to overspeed during climbout

The old code relies on the action of the integrator to raise the nose above the minimum pitch angle which depending on the model and the tuning can be too slow to correct. Biasing the pitch angle to climbout minimum will reduce the taken before an overspeed condition is corrected.
SITL: added SIM_RC_FAIL

simulate RC failure with no signal
HAL_SITL: use SIM_RC_FAIL
Plane: allow throttle failsafe on no RC input

on PX4 we just stop getting input on loss of RC - we need to consider
this to be "throttle failsafe"
Plane: only allow right rudder for arming

copter users may try to use left rudder to ensure aircraft is
disarmed. Making left rudder arm could be dangerous
Rover: check for failed RC input

loss of RC for 2s is considered a throttle failsafe
Plane: added FS_GCS_ENABL==2 option

this allows GCS failsafe when the GCS isn't getting updates from the
aircraft
Plane: make the defaut for FS_GCS_ENABL clearer
RC_Channel: added disable_out() method
AP_Arming: make enum values clearer
Plane: fixed ARMING_REQUIRED=2 on APM2 to disable rc output on throttle
Plane: reset mission on disarm

this makes repeated missions easier