Listenbrainz scrobbling (#1424)

* 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

conf/configuration.go

@@ -74,6 +74,7 @@ type configOptions struct {
 	DevSidebarPlaylists        bool
 	DevEnableBufferedScrobble  bool
 	DevShowArtistPage          bool
+	DevListenBrainzEnabled     bool
 }
 
 type scannerOptions struct {
@@ -241,6 +242,7 @@ func init() {
 	viper.SetDefault("devenablebufferedscrobble", true)
 	viper.SetDefault("devsidebarplaylists", true)
 	viper.SetDefault("devshowartistpage", true)
+	viper.SetDefault("devlistenbrainzenabled", false)
 }
 
 func InitConfig(cfgFile string) {