Renamed /new-room endpoint to /add-room/new

This has been done in an effort
to move all endpoints used to join a room
under one umbrella (/add-room)

A list of planned or completed endpoints:
- /add-room
- /add-room/new
- /add-room/by-id

lib/main.dart

@@ -21,7 +21,7 @@ final routesUnauthorized = RouteMap(routes: {
 // routes when user is logged in
 final routesLoggedIn = RouteMap(routes: {
     '/': (_) => const MaterialPage(child: HomePage()),
-    '/new-room': (_) => const MaterialPage(child: NewRoomPage()),
+    '/add-room/new': (_) => const MaterialPage(child: NewRoomPage()),
     '/add-room': (_) => const MaterialPage(child: JoinRoomPage()),
     '/r/:server/:tag/:page?': (info) => MaterialPage(
       child: RoomPage(info.pathParameters['server'] ?? "",

lib/screens/room/join.dart

@@ -373,7 +373,7 @@ class _JoinRoomPageState extends State {
         icon: const Icon(Icons.add),
         onPressed: () {
           // create new room
-          Routemaster.of(context).push("/new-room");
+          Routemaster.of(context).push("/add-room/new");
         },
         tooltip: 'Create Room',
       ),