AirspaceManager is now exposed by QGroundControlQmlGlobal instead of Vehicle (available all the time)

Added an "unavailable" icon for when no vehicle is connected
Toggle restriction overlays (map) on/off based on the airspace widget being expanded/collapsed respectively

Added an "unknown" weather icon for when I get "valid" data and no icon

Eliminated flight widget "states"
Define flight widget top margin (plugin options)