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

Also updated all the units for the heartbeat values that are exposed to the realtime plotter to follow the suggestions laid out by the documentation for valueChanged().

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().

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

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

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

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.

Added support for reading uint8 values from an autopilot via QGC. Still need to add support for writing them.

Added visualization of obstacles. Fixed relative font path issue in 3D widgets by using QFont within osgText::Font instead of using static font filename.

Enabled visualization of point cloud data via Protocol Buffers serialization and extended_mavlink_message.