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