Ardrone actions

These commits add basic support for the Parrot AR Drone and should not change the behavior for any other autopilot.  Merging this should also close issue 919, but I'm not sure how to associate that issue with this pull request.
Which code are you suggesting moving and to which ChangeFlightMode method (there are 2)?  Just loiter or all actions?  And I don't understand why it doesn't belong here.  The AR Drone doesn't use custom modes for actions.  It uses these standard action commands.  In addition, if all of these if statements move to one of the ChangeFlightMode methods, we will have to repeat a similar case statement to map ApmModes to commands.