Redirect to token revoked page when the realtime connection sees a fa…

…ilure

This way people get some context for why they got kicked out during the Gitter migration,
see element-hq/roadmap#26

public/js/components/realtime.js

@@ -77,7 +77,7 @@ var accessTokenFailureExtension = {
         window.alert(
           `Realtime communications with the server have been disconnected. ${message.error}`
         );
-        logout();
+        logout('/login/token-revoked');
       }
     }