- Update version to 1.26.0
* Translations update
* replace mute/unmute checkmenuitem with imagemenuitem
* re-generate po files
* update copyright to 2021
* man page: mate-volume-control-applet.1 -> mate-volume-control-status-icon.1.
* Fix desktop file validation warnings
* remove dead function mate_panel_applet_set_background_widget