Fixed bugs the unit test found

Also fixed bug with ArduPilot guided waypoint write which would trash
existing mission.

Remove/comment off debug output pollution

This time to handle correctly updating plan/fly view when plan changes

Works around ArduPilot strangeness with empty missions end

Must memset structures before use.

Fixed a pile of bugs as well

Plus low battery announce changes

Retry in all the right/possible places. Don’t freak out about things
coming in unknown sequences.

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