Store improvements

- Store games by source
- Added convenience dunder methods (contains, iter, len, getitem)
- Added store.get
- Changed `enable_in_pipeline` for `toggle_in_pipeline`

src/window.py

@@ -117,7 +117,7 @@ class CartridgesWindow(Adw.ApplicationWindow):
     def set_library_child(self):
         child, hidden_child = self.notice_empty, self.hidden_notice_empty
 
-        for game in shared.store.games.values():
+        for game in shared.store:
             if game.removed or game.blacklisted:
                 continue
             if game.hidden: