Add an option to sort the room list by recents first

Fixes https://github.com/vector-im/riot-web/issues/8892

src/settings/Settings.js

@@ -1,6 +1,6 @@
 /*
 Copyright 2017 Travis Ralston
-Copyright 2018 New Vector Ltd
+Copyright 2018, 2019 New Vector Ltd.
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -340,4 +340,9 @@ export const SETTINGS = {
         displayName: _td('Show developer tools'),
         default: false,
     },
+    "RoomList.orderByImportance": {
+        supportedLevels: LEVELS_ACCOUNT_SETTINGS,
+        displayName: _td('Order rooms in the room list by most important first instead of most recent'),
+        default: true,
+    },
 };