Add ServerNoticeButton to UserEditToolbar

For this, the feature "Server Notices" must be activated on the server.

Change-Id: If3873dc5548822a06a7be0c55e48835c9fb8f78f

src/App.js

@@ -37,6 +37,7 @@ const App = () => (
     />
     <Resource name="rooms" list={RoomList} icon={RoomIcon} />
     <Resource name="connections" />
+    <Resource name="servernotices" />
   </Admin>
 );