Initial support for global plan-wide altitude mode setting

Rework handling of fw/vehicle type with respect to conflicts with actual vehicle types.

VTOL Takeoff should be considered a transition to FW

Fix VTOL hover determination

Fix logic of when adding Landing item is allowed

Add support for Json file string translations

Major rework to support terrain profile display and terrain collision reporting

VTOL Landing Pattern support

Drag of land/loiter maintains land distance/heading as appropriate

Out Survey polygons with KML save

Much better mission->kml conversion support

Remove buggy support for generation of incomplete lines

Correct handling of terrain ready when loading back from file

Plan: Add support for takeoff item required

Fix ArduPilot fake home position handling

Mavlink terrain protocol support

Avoid arrow positioning with take item

Fix current item updating after delete

Fix Plan insert Takeoff/Land for correct enable state and insert into correct place. 

Update vehicle heading from possible item change

Add support for incomplete segment visuals

When a child item is current show the parent as selected

Support move item to previous item position

Active ROI indication in Plan Map items

Cancel ROI support plus many big fixes

More takeoff item fixes

Fix for vehicle based home position management

New user model for Takeoff item

Fix incorrect usage of _settingsItem causing crashes

More work on contextual Plan tools

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

More work getting _addMissionSetting right

Fix handling of _addMissionSettings