forward: Add description extension to geo uri

Android and Google Maps support an extention to geo uri that allows
specifying a label to a location.

The form is
    geo:0,0?q=lat,lng(label)

This patch adds parsing of that format to GeocodeLocation.

https://bugzilla.gnome.org/show_bug.cgi?id=727861
test-geouri: fix memory leaks

https://bugzilla.gnome.org/show_bug.cgi?id=727861
forward: fix memory leaks

https://bugzilla.gnome.org/show_bug.cgi?id=727861
forward: Document geo URI scheme usage

https://bugzilla.gnome.org/show_bug.cgi?id=727861