Add message to indicate /routes is not implemented (#77)

If someone clicks on Routes in the sidebar, the page appears to fail to load, 
but this endpoint is unimplemented. Add a message to indicate that.

web/app/js/components/Routes.jsx

@@ -8,7 +8,8 @@ export default class Routes extends React.Component {
         <div className="page-header">
           <h1>Routes</h1>
         </div>
+        <div>Coming soon!</div>
       </div>
     );
   }
-}
+}