Allow for app downgrade #127
Description
The sync query might provide an older version of the app, by providing an old release_key.
Whenever the release_key given by the sync query does not coincide with the existing release_key of the app, then the existing app container and image on the device should be deleted from the device and the new version should be installed.
The app state should eventually be the target_state given in the sync query.
The corresponding issue in the frontend is RecordEvolution/RESWARM#4592