Cache listen submissions when ListenBrainz is currently not reachable

[lyarenei]

Some ideas/specifications:

• Cache persistency: it is possible to create files from plugins, so that should be doable
• Resubmitting listens: a daily scheduled task should do the job (there's always an option to run it manually)
• Syncing favorites: probably not possible unless there's an easy and reliable way to retrieve MSIDs

Otherwise cache all metadata, or try pulling from MusicBrainz again if it was not reachable at the time of caching