One single major bug left for the flat map and the flat map is now as fast as the globe.

* src/lib/MeasureTool.cpp: degX,Y -> lon, lat

* src/lib/MarbleWidget.cpp:
- Some fix by Jan Becker about screenCoordinates(...)
- degX,Y -> lon, lat
* src/lib/VectorMap.{h,cpp}:
- Speedup by avoiding Quaternion representation for
rectangular projection
- degX,Y -> lon, lat
* src/lib/PlaceMarkLayout.cpp:
- Fixing "two few placemarks" bug for rect. projection
- Speedup by avoiding Quaternion representation for rect. projection
- degX,Y -> lon, lat