* add SubsonicScrobbler, add Scrobble method in SubsonicService
* new class SubsonicScrobbleRequest, use queue again, clean up
* add checkbox to enable server-side scrobbling to Subsonic settings page
* Check serversidescrobbling in SubsonicScrobbler::ReloadSettings instead of SubsonicService
TODO: SubsonicScrobbler::ReloadSettings needs to be called when
SubsonicSettings change.
- Improve album cover manager
- Change art_automatic and art_manual to QUrl
- Refresh collection album covers when new album covers are fetched
- Fix automatic album cover searching for local files outside of the collection
- Make all Json services check HttpStatusCodeAttribute
- Show detailed SSL errors for Subsonic, Tidal and Qobuz