fix(frontend): fix encoding of queryparameters in api calls

We had a bug where the "+" before the timezone in ISO8601 strings was
being parsed as " " in the server because it was not properly encoded.

By using URLSearchParams to create our querystring we should be fine.

frontend/src/util/queryString.ts

@@ -0,0 +1,12 @@
+interface QueryParameters {
+  [x: string]: string;
+}
+export const qs = (parameters: QueryParameters): string => {
+  const queryParams = new URLSearchParams();
+
+  Object.entries(parameters).forEach(([key, value]) =>
+    queryParams.append(key, value)
+  );
+
+  return queryParams.toString();
+};