Added some values from the HEARTBEAT and SYS_STATUS messages to realtime plotter

Message Inspector displayed always 0 Hz for Heartbeat

fixes segfault in local 3D view when starting QGC without having a UAS selected

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().

Increased GPS sat timeout from 1 second to 10 seconds

Exposed HEARTBEAT.system_status and HEARTBEAT.base_mode to the realtime plotter widget via the valueChanged signal.

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

Various changes

Conflicts:
	qgroundcontrol.pri
	src/uas/UAS.cc

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

Added a workaround to the mission management code where it would only accept messages addressed to the MAV_ID_MISSIONPLANNER component. This was causing problems with the send-loss value being calculated, so I decided to add this until a proper solution can be developed.

Refactored part of MAVLinkProtocol::receiveBytes() as I was trying to debug within it. Nothing major, though I did remove an unnecessary loop.