Improve room setting

* Port away from OverlaySheet
* Use Kirigami.CategorizedSettings
* Add join rules (read only for now)

src/CMakeLists.txt

@@ -36,6 +36,7 @@ add_executable(neochat
     spellcheckhighlighter.cpp
     blurhash.cpp
     blurhashimageprovider.cpp
+    joinrulesevent.cpp
     ../res.qrc
 )