Change Command only supported for Simple Items

Fix editor sizing

This is in addition to the existing text edit control.

This way you can click anywhere

* Load Plan
* Save to KML
* Load Plan (it tries to load KML instead)

Create new, specific button for clearing mission from vehicle
Adjust sizing of DropPanel

This was too confusion to expose since QGC currently does not support ArduPilot terrain tile send.

More commonly known terminlogy