Fixed error (in VS2010) about lacking a return value introduced in 6a55b6cd.

Introduced persistence in RGBDview, needs debugging, fixed a bug in param reading in the simulator, pushed message sender a bit forward, not working yet

Removed outdated MAVLINK v0.9 version as QGC does not work with this version. Added feature to import COLLADA terrain model and visualize model in 3D view.

cause: check for null pointer had no effect (static memory)
solution: fill mavlink messages (and thus) message type with 0xff. this patch assumes that message ID 0xff is never used
positiv side effect: qgroundcontrol uses 2% less cpu on my machine (eeepc)

Removed some dead code.
Added more valueChanged() signals to account for every data type. This moves the conversion over into the valueChanged receivers, which while it will require more slot-functions, makes it easier to add more code as any necessary conversion is done internally to the slot and so the signaler doesn't need to know the details.
I also added some more details on the types of units expected by valueChanged().

sending GPS sat information via a low-bandwidth link like the UM96 @ 9600 baud should also work at low frequencies like 0.2 Hz

Changed the drop rate from a SYS_STATUS message to follow the MAVLink specs along with some extra range checking.

Added multi-UAS support to QGCRGBDView. Fixed display timeout issue on computer for which data source is not time-synchronized.

Code changes to reflect new header information (sysid, compid, timestamp) in protobuf messages. Added protobuf message timeout; old messages will not be visualized. Fixed getParameterValue in ParamManager; the method can segfault if the component id or parameter id is not valid.

Also removed redundant code in QGCMapWidget.cc.