ui: Allow hotkey control

It can now be controlled how to handle hotkey callbacks.
Additionally this new functionality is now used to disable hotkeys when
the screen is locked.

rhbz#911680

Change-Id: I8e03dc250838a8737748a065f64cad5c5244bb24
Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>
bump version to 2.6.1

Change-Id: I7f97218c0b10dc141d0443eedf304b1181ff6bb5
Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>