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

Includes ability to load params

- GeoFence support comes from plugin
- Circle fence support
- Better param support

Plus new unit tests

# Conflicts:
#	src/MissionManager/MissionManagerTest.cc

- override by vehicle type
- override by firmware type

Previous order was signalling new mission items available prior to in
progress going false. This was causing MissionController to pull an
empty mission list.

Instead us a Toolbox concept which hangs off of QGCApplication