Make sure important errors are always shown to the user

Summary:
This diff makes sure that important errors are always shown to the user, such as an xcode version mismatch.

Also made some small styling improvements

Reviewed By: jknoxville

Differential Revision: D19660337

fbshipit-source-id: 24dfb4d98bfdd1666164403f87b6a4e1dc915ddb

src/dispatcher/server.tsx

@@ -46,10 +46,12 @@ export default (store: Store, logger: Logger) => {
       err.code === 'EADDRINUSE'
         ? "Couldn't start websocket server. Looks like you have multiple copies of Flipper running."
         : err.message || 'Unknown error';
+    const urgent = err.code === 'EADDRINUSE';
 
     store.dispatch({
       type: 'SERVER_ERROR',
       payload: {message},
+      urgent,
     });
   });