Plus low battery announce changes

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

Convert bool settings to SettingsFact

Use component id from heartbeat

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.