* Refactor session_keys to its own package
* Adjust play_tracker
- Don't send external NowPlaying/Scrobble for tracks with unknown artist
- Continue to the next agent on error
* Implement ListenBrainz Agent and Auth Router
* Implement frontend for ListenBrainz linking
* Update listenBrainzRequest
- Don't marshal Player to json
- Rename Track to Title
* Return ErrRetryLater on ListenBrainz server errors
* Add tests for listenBrainzAgent
* Add tests for ListenBrainz Client
* Adjust ListenBrainzTokenDialog to handle errors better
* Refactor listenbrainz.formatListen and listenBrainzRequest structs
* Refactor agent auth_routers
* Refactor session_keys to agents package
* Add test for listenBrainzResponse
* Add tests for ListenBrainz auth_router
* Update ListenBrainzTokenDialog and auth_router
* Adjust player scrobble toggle
See https://pkg.go.dev/github.com/robfig/cron#hdr-CRON_Expression_Format for expression syntax.
`ScanInterval` will still work for the time being. The only situation it does not work is when you want to disable periodic scanning by setting `ScanInterval=0`. If you want to disable it, please set `ScanSchedule=""`
Closes#1085