Get team_token from the RTS on login

Use the /login endpoint of the RTS to get the team token when the user has successfully logged in.

src/RtsClient.js

@@ -77,4 +77,14 @@ export default class RtsClient {
             }
         );
     }
+
+    login(userId) {
+        return request(this._url + '/login',
+            {
+                qs: {
+                    user_id: userId,
+                },
+            }
+        );
+    }
 }