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

cmd/root.go

@@ -80,6 +80,9 @@ func startServer() (func() error, func(err error)) {
 			if conf.Server.LastFM.Enabled {
 				a.MountRouter("LastFM Auth", consts.URLPathNativeAPI+"/lastfm", CreateLastFMRouter())
 			}
+			if conf.Server.DevListenBrainzEnabled {
+				a.MountRouter("ListenBrainz Auth", consts.URLPathNativeAPI+"/listenbrainz", CreateListenBrainzRouter())
+			}
 			return a.Run(fmt.Sprintf("%s:%d", conf.Server.Address, conf.Server.Port))
 		}, func(err error) {
 			if err != nil {