adjust frontend to new backend

templates/api/exception.mustache

@@ -0,0 +1,15 @@
+/**
+ * Represents an error caused by an api call i.e. it has attributes for a HTTP status code
+ * and the returned body object.
+ *
+ * Example
+ * API returns a ErrorMessageObject whenever HTTP status code is not in [200, 299]
+ * => ApiException(404, someErrorMessageObject)
+ *
+ */
+export class ApiException<T> extends Error {
+    public constructor(public code: number, message: string, public body: T, public headers: { [key: string]: string; }) {
+        super("HTTP-Code: " + code + "\nMessage: " + message + "\nBody: " + JSON.stringify(body) + "\nHeaders: " +
+        JSON.stringify(headers))
+    }
+}