Add more UI events and get backend threaded up.

src/WebInterface.h

@@ -35,6 +35,8 @@ public:
     void songChangedFromServer(AudioTrack* nextTrack);
     void skipVotedFromServer(User* userRequestingToSkipCurrentTrack);
     void voteUpdateFromServer(User* userVoting, bool forSkip);
+    void voteNextSongFromServer(User* userVoting, AudioTrack* trackVoted);
+    void voteNextPollClosedFromServer();
 private:
     struct internal;
     internal* priv_int = 0;