Per app location permission for flatpaks

With geoclue fixed (Librem5/debs/geoclue-2.0!2 (merged)) flatpaks now prompt for permission to sue location services. This adds the necessary dialog ()

We currently don't store permissions in the xdg permission store which can happen as a follow up.

See https://social.librem.one/@agx/105911859823532194

We might want to swap the subtitle and body but then the question isn't right above the buttons.

Closes: #524 (closed), #532 (closed)