Mavlink terrain protocol support

When a child item is current show the parent as selected

Support for new TakeoffMissionItem and Takeoff Tool 

Wizard Mode for Create Plan

Don't query terrain if no location

Don't query intermediate state

Fix failure handling

* Flight modes still not implemented. Waiting on message change.
* Also includes various cauterization of UI things which should not be
available on high latency link.

Signed-off-by: Patrick José Pereira <patrickelectric@gmail.com>

Plus many load/save fixes

Plus new unit tests