Even though it hasn't been supported forever, the files where still
being compiled

Prevent shutdown ordering crashes

* Make MainToolbarIndicators reusable by other views
* Change to font based ratio sizing

This prevent the visibility change from trashing source setting

Shows horizontal/vertical scroll indicators

* Vehicle selection must be global control
* Disconnect controls must be associated with Vehicle

Made QGCCorePlugin derive from QGCToolBox and expose everything through the same mechanism as everything else.

Also removed intermediate param load retry message

Moving source files into Vehicles as it is a more coherent place.

Forcing QGC to use Mavlink V2 if vehicle supports it.

This makes it available on mobile builds

Too buggy to leave in for now

Also added new FirmwarePlugin::brandImage support

No signing support yet