Various improvements to DataPlot and Communication configuration window

Bind support for DSMX with 8 or more channels

* The "Simulation" option is now not selectable.
* If the link is a simulation, then you can't change it to a different link type.
* The OPAL option is not shown if support is not compiled in.
* Fix the buddy, tab order and accelerators in the GUI.

Do not crash in an empty symmetric IncrementalPlot

This crash could be reproduced by starting QGroundControl, switching to
plot, then clicking the "Symmetric" checkbox.

Sensor Hil for flightgear

Quadrotor HILS Update

This commit disabled RC RAW signal callback.

Fix toolbar battery voltage not updating

Implement message driven receiver pairing