It's time we switch to GTK 4

[Keruspe]

I think the steps will be:

• Comment out all clipboard/clipboards-manager/gdkatom stuff (yes, this will break the linkage).
• Make the rest build properly
• Uncomment gradually what has been commented, porting stuff along the way.

We should definitely do that before the v40 release

[Keruspe]

basic daemon with text-only support working as of now