Implement currentPlaylistService, queueService, and playlistService

@deini @malucky 

The playlistService has not been implemented fully because we'll need to work on the userService first, but we can at least add to it the repo at this point. 
i think if we're commenting with `@param` already might as well pass the type, and I think {Object} for consistency is good instead of {Playlist}. In the description it describes what kind of object it is anyway