mavproxy_cmdlong.py should include all commands supported by ArduPilot

MAVProxy supports MAV_CMDs by implementing functions in [mavproxy_cmdlong.py](https://github.com/Dronecode/MAVProxy/blob/master/MAVProxy/modules/mavproxy_cmdlong.py). Currently only a small subset of commands has been implemented - this should include all commands that ardupilot supports.

The current set implemented is
- MAV_CMD_NAV_TAKEOFF
- MAV_CMD_DO_CHANGE_SPEED
- MAV_CMD_CONDITION_YAW
- set_position_target_local_ned_send

Additionally, these are sent with what appears to be rubbish values.
- MAV_CMD_DO_DIGICAM_CONFIGURE,
- MAV_CMD_DO_DIGICAM_CONTROL

The full set of commands that are handled by Copter in [GUIDED mode is here](http://dev.ardupilot.com/wiki/copter-commands-in-guided-mode/). I don't have a list for those that can be sent in Rover/Plane. The full list of [AUTO commands are here](http://planner.ardupilot.com/wiki/common-planning-a-mission-with-waypoints-and-events/common-mavlink-mission-command-messages-mav_cmd/)

Start in MAVProxy/modules/mavproxy_cmdlong.py and compare its implemented MAV_CMD handlers with the ArduPilot Copter GUIDED-mode and AUTO command lists linked in the issue. Define the supported command set for Copter, Plane, and Rover, correct the digit-camera command values, and verify that every targeted command is represented and sends meaningful parameters.

Written by the indexing model from the issue text.