Initial breakout for room list rewrite

This does a number of things (sorry):
* Estimates the type changes needed to the dispatcher (later to be replaced by https://github.com/matrix-org/matrix-react-sdk/pull/4593)
* Sets up the stack for a whole new room list store, and later components for usage.
* Create a proxy class to ensure the app still functions as expected when the various stores are enabled/disabled
* Demonstrates a possible structure for algorithms

src/settings/Settings.js

@@ -131,6 +131,12 @@ export const SETTINGS = {
         supportedLevels: LEVELS_FEATURE,
         default: false,
     },
+    "feature_new_room_list": {
+        isFeature: true,
+        displayName: _td("Use the improved room list component (refresh to apply changes)"),
+        supportedLevels: LEVELS_FEATURE,
+        default: false,
+    },
     "feature_custom_themes": {
         isFeature: true,
         displayName: _td("Support adding custom themes"),