Enable the new room list by default and trigger an initial render

We have to trigger an initial render because during the login process the user will have started syncing (causing lists to generate) but the RoomList component won't be mounted & listening and therefore won't receive the initial lists. By generating them on mount, we ensure that the lists are present once the user gets through the login process.

src/settings/Settings.js

@@ -150,7 +150,7 @@ export const SETTINGS = {
         isFeature: true,
         displayName: _td("Use the improved room list (will refresh to apply changes)"),
         supportedLevels: LEVELS_FEATURE,
-        default: false,
+        default: true,
         controller: new ReloadOnChangeController(),
     },
     "feature_custom_themes": {