Use component id from heartbeat

Change in visibility was causing combo box contents to reset. Visible
goes to false even when you move away from Plan view, not just when the
combo is unused.

- Incorrect signaling causing dirty but to be incorrect
- Remove all not working
- Min fence point count incorrect

Also added new FirmwarePlugin::brandImage support

_finalize methods need information which is not available if all you
have is a mavlink_message_t

before, with a version of eg. 1.5.0, the user was wrongly notified.