Port geoclue plugin to GeoClue version 2.x

The current geoclue position plug-in uses GeoClue v0.12. This version is very old and uses a glib based wrapper. The latest major version is 2.0 and was introduced in September 2013. This version has a dbus interface only.

From a Qt perspective it is much more desirable to remove the glib wrapper library. Interaction with the glib event loop can cause problems with Qt's event loop and in general we are reducing the dependency chain of the position plug-in.

For the foreseeable future the geoclue 0.12 plug-in must continue to exist.