This is a bugfix release. It also extends the tests to icons.
Bugs fixed:
* Fix missing Gtk+ themes path in dist_themes variable (Bug #12831)
* Fix theming for callback button in notifications (Bug #12841)
* Don't show notification buttons without text (Bug #12834)
* Support image-path hint of the fd.o spec (Bug #7846)
* Fix priorities of icon handling according to the fd.o spec
* Make icon-size of fallback consistent with all other notifications
Updated translations: Croatian, Lithuanian, Malay, Thai