If Facts are referenced from FactPanelController, we need to reference
count the AutoPilotPlugin such that it doesn’t get destroyed until
after the FactPanelController is destroyed.

This prevents the indicator from overlapping the “Flight Modes” text

- You can now cancel parameter change
- Tablete friendly

Also removes qextserialport

Also updated parser for new xml format

Use default font wherever possible. Where that doesn’t work, use
ScreenTools::dpiAdjustPointSize.

More consistent with Qml usage pattern

Also many LinkManager API changes to further isolate all link
management inside LinkManager.

Switch QGC firmware upgrader for PX4 to AWS and Travis. Use beta/stable/master for Firmware, map all three items to master for Flow (because there are not beta/stable branches)