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

ui/src/player/PlayerEdit.js

@@ -48,7 +48,7 @@ const PlayerEdit = (props) => (
         ]}
       />
       <BooleanInput source="reportRealPath" fullWidth />
-      {config.lastFMEnabled && (
+      {(config.lastFMEnabled || config.devListenBrainzEnabled) && (
         <BooleanInput source="scrobbleEnabled" fullWidth />
       )}
       <TextField source="client" />