Provide geo-fencing functionality

The location infrastructure should offer a way for applications to setup and maintain geo-fences (see [1]).

As usual, the respective functionality should be guarded by app confinement and require the user to approve the
respective transaction via our trust infrastructure. In addition, the location infrastructure should be clever in filtering
out requests that would enable an app to escape its lifecycle boundaries.

For that, the following changes would be required throughout the stack:

[1.] Geo-fencing capabilities of h/w should be exposed via the platform-api HW interfaces: See http://androidxref.com/5.1.1_r6/xref/hardware/libhardware/include/hardware/gps.h#1014

[2.] The location-service should expose geo-fencing capabilities on the location::Service::Session objects.

[3.] The platform-api should expose an app-facing itf modelling geo-fencing functionality.

[4.] qtubuntu-sensors should provide an implementation of http://doc.qt.io/qt-5/qgeoareamonitorsource.html