adjust frontend error handling, add client/server mismatch middleware

client/homebrew/utils/request-middleware.js

@@ -0,0 +1,12 @@
+const request = require('superagent');
+
+const addHeader = (request)=>request.set('Homebrewery-Version', sessionStorage.getItem('version'));
+
+const requestMiddleware = {
+	get    : (path)=>addHeader(request.get(path)),
+	put    : (path)=>addHeader(request.put(path)),
+	post   : (path)=>addHeader(request.post(path)),
+	delete : (path)=>addHeader(request.delete(path)),
+};
+
+module.exports = requestMiddleware;