Migrate to gtk4 / libadwaita
It's time to start a new migration to the new version of the Gtk library. We need to make use of the new modern Gtk4 lib and libadwaita to support dark theme.
TODO
-
Build with gtk4 -
Remove gspell -
Remove GtrNotebookwidget -
... -
Find a replacement for gspell (this could be optional, we can drop the spellcheck support until gspell support gtk4) -
Clean the code (remove commented code, debug printf and -oldfiles)