Add a custom Coordinate type

Can be used is a duck-typed replacement for the Coordinate type provided by QtPositioning
if QtPositioning is not available.
Add QML Location module for the Qt5 GUI

The location module:
* works with Qt 5.1+ (on Qt 5.1 a dummy position source is used)
-> this means it work just fine id QtPositioning is not available
   for some reason
* supports NMEA file position source for debugging
* forwards position data to Python
* computes bearing from last two position updates
Use the new Location QML module
Process position updates from QML

The Qt5 QML GUI currently gets position data from the QML positioning
interface, which then pushes the position updates to Python.