Clean up references to MainRootWindow globals

Rework Fly View into separate layers which can be customized at each layer.

CP - If GCS starts receiving its own coordinates, don't change the map center if it is already tracking the vehicle.

Heading value should be real so NaN comes through

Get rid of QGCView, QGCViewPanel and FactPanel. All messages and dialogs are now handled in the root window.

Add Distance to GCS to Vehicle FactGroup

Plus low battery announce changes

* Map type now set from General settings
* No map type control in maps