Pathplanner improvements

So this is based on comments here https://groups.google.com/forum/#!topic/phoenixpilot/47Qw0FEltH4

It includes making the mode selector work more cleanly and the model now allows editing NED representations while keeping a single internal representation.  This has the down side that the path itself (on the GCS side) is still an absolute one.  That means if the home location is moved then the positions (relative) will all be recalculated.  However, the representation on the UAV is relative so if they are uploaded, then the home location changes, then downloaded it will move the path.

A future improvement will make the GCS side representation selectable and possible the UAV side too.

The locked attribute for waypoints was removed and this is probably overkill and should be restored.