Port to Gtk4

[danirabbit]

Fixes #224

Obviously doesn't work because none of the plugs have been ported but it's a start :)

todo:

• [x] Port window size save/restore
• [x] Fix shutdown connect
• [x] See if we can use .rich-list for search
• [x] Press enter in search to activate first item
• [x] Press down in search to move focus to category view
• [x] Press escape in search to clear search entry
• [ ] Fix mouse back button
• [x] Fix type to search
• [x] Figure out why most of the categories are invisible

[danirabbit]

Making a note that back navigation with the mouse button works already, but it requires pressing the button twice. Maybe something is swallowing these events?

[danirabbit]

Let's fuckin go