New user model for Takeoff item

More work on contextual Plan tools

A contextual Land/RTL tool. Better waypoint line calc.

More work getting _addMissionSetting right

Fix handling of _addMissionSettings

Support for new TakeoffMissionItem and Takeoff Tool 

Fix save state checks. Show overlay on New.

Wizard Mode for Create Plan

New Create Plan support

Fix SplitSegment insertion

Allow split of current segment

Remove unnecessary signaling

Use QmlObjectListModel::begin/endReset to keep Qt from blowing it's brains out with too many updates

Fix initial load for Plan view

Fix missing waypointLinesChanged signal. Remove unnecessary directionArrowChanged signal.

More work on direction arrows

Expose complex item names in a way useful for custom builds

Support custom build override of available complex items

Fix planned home position set when takeoff has no coordinate in it

Fix resume mission item count bug

Make all argument to AirMap queries based on what the screen shows (bounding rectangle and/or radius), respecting the limits imposed by AirMap.

Otherwise things like gimbal angles end up on the wrong items.