gtk3:Some MATE integragion and backporting bits from gtk4 version

[mark-herbert42]

1. Left click on battery opens mate battery statistics dialog
2. Left click on volume open mate volume control dialog with advanced device selection, output/input profiles etc.
3. Backported language widget - now it shows keyboard language and allows to change with mouse click
4. Implemented panel unhide on keyboard language change and volume mute/unmute with keyboard shotcut
5. Backported configurable panel hide-unhide duration,
6. Added notification center size config options.