Migrating away from GTK3 and Glade

[C0rn3j]

This is mostly a placeholder issue.

Glade is unmaintained since 2022 and only for GTK3.
Also not very well liked - https://blogs.gnome.org/christopherdavis/2020/11/19/glade-not-recommended/
There is a bunch of deprecations in the current Glade files, but that's probably besides the point with the major migration needed.

Aside from closing our eyes and ignoring the issue, there are two avenues we can take, both of which require us to move away from Glade:

• Port to GTK4
  • there was an attempt in upstream, but author lost interest when they found out the project is supposed to be rewritten - Port to GTK4 kozec/sc-controller#706
  • upstream porting guide is here - https://docs.gtk.org/gtk4/migrating-3to4.html
• Port to another toolkit like Qt6

I have at least for the time being bumped up the version notes for 3.24 and re-saved the Glade files - a96b9de

GTK5 is in development, so hopefully someone can push for this before that, as GTK3 is supposed to be killed off when GTK5 releases.