Restrict map providers for iOS.

QGCCommon.pri

ios/iOS-Info.plist

src/FlightMap/FlightMapSettings.cc

src/FlightMap/FlightMapSettings.h

src/QtLocationPlugin/QGCMapEngine.cpp

src/QtLocationPlugin/QGCMapUrlEngine.cpp

src/QtLocationPlugin/QGCMapUrlEngine.h

src/QtLocationPlugin/QGeoCodeReplyQGC.cpp

src/QtLocationPlugin/QGeoTiledMappingManagerEngineQGC.cpp

src/ui/preferences/GeneralSettings.qml