Support for cache in reconstructions, non-required cache added to exports, playlists shares now add a cache aswell for quicker importing

New auto-backup storage using the Storage Access Framework, minor dialog tweaks, minor settings ui tweaks

Fixed retryDialog button ordering. Fixed default action on confirmation dialog. Set notifications to be silent. AddToQueue button implemented on channel fragment. Added confirmation for deleting downloaded playlist videos. Separately handled UnknownHostException to prevent the dialog from showing when offline.