depends on GLib 2.37

Needed for the latest GDbus code gen.

https://bugzilla.gnome.org/show_bug.cgi?id=706627
add empathy-geoclue-helper

Based on a proposed API on fdo#68658. May end up in geoclue at some point.

https://bugzilla.gnome.org/show_bug.cgi?id=706627
location-manager: use Geoclue 2

https://bugzilla.gnome.org/show_bug.cgi?id=706627
preferences: remove location sources preferences

Not used anymore with Geoclue 2.

https://bugzilla.gnome.org/show_bug.cgi?id=706627