FirmwarePlugin: Issue a warning upon connecting if the firmware in use is not using a stable release

Remove/comment off debug output pollution

Just use settings defaults

Previous version would require plugin to override all the
isFooFlightMode methods to work correctly. Now just change mode name
and regular plugin code works correctly.

This way third parties can use PX4FirmwarePlugin as base class and
override as needed

Use component id from heartbeat

Also added new FirmwarePlugin::brandImage support

Also change Plan Element selection ui