AppListFragment: Fix back button in AppDetailFragment not tracking back to AppListFragment.

app/src/main/java/de/ccc/events/badge/card10/hatchery/AppListFragment.kt

@@ -69,6 +69,7 @@ class AppListFragment : Fragment() {
         val fragmentManager = activity?.supportFragmentManager ?: throw IllegalStateException()
         fragmentManager.beginTransaction()
             .replace(R.id.fragment_container, fragment)
+            .addToBackStack(null)
             .commit()
     }