Chore(challenges): separate code storage sagas

common/utils/combine-sagas.js

@@ -0,0 +1,9 @@
+import { Observable } from 'rx';
+
+export default function combineSagas(...sagas) {
+  return (actions$, getState, deps) => {
+    return Observable.merge(
+      sagas.map(saga => saga(actions$, getState, deps))
+    );
+  };
+}