Mavlink terrain protocol support

Plugin'ized follow me support

Instead of trying to keep a vehicle type within the FirmwarePlugin instance, pass the vehicle to the function so it can query the type that way.

Smart RTL support

Remove the concept of reserved buttons for manual control

Add gotoFlightMode method

Add support for Orbit flight mode

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