RC_Channel_aux: add epm to servo function enum
EPM: add support for ver2, remove support ver 1
Copter: integrate EPM ver2
EPM: add params for pwm levels add re-grab feature

Also include some minor commenting changes
Copter: remove EPM neutral from ch7/ch8 switch

The EPM library returns the pwm output sent to the EPM to the neutral
position automatically meaning an explicit ch7/ch8 setting is not
required
GCS_MAVLink: generate run on master
GCS_MAVLink: version updates after generate
GCS_MAVLink: generate after move of PARACHUTE_ACTION
GCS_MAVLink: version update after generate
GCS_MAVLink: add MAV_CMD_DO_GRIPPER
GCS_MAVLink: generate after adding DO_GRIPPER
GCS_MAVLink: version update after adding DO_GRIPPER
Mission: add support for DO_GRIPPER
Copter: add support for DO_GRIPPER command
Copter: enable EPM by default on Pixhawk
Copter: add support for DO_PARACHUTE from GCS

Mission command support was already included but this adds support for
DO_PARACHUTE received as a COMMAND_LONG message which are sent from the
GCS when the command should be executed immediately
Copter: set sys_status motor outputs bit from safety switch
Copter: allow GCS to turn safety switch on/off
AP_HAL: add force_safety_on method
HAL_PX4: implement force_safety_on