Resume last playlist

An option to resume last playlist would be nice to have, so I started work on this.

We check if the document.referer is not tubalr.com and that we're visiting /. If so, we restore the latest playlist using the existing History object.

This still needs a little work:
* The settings text needs to be updated and playlist should preserve order. 
* Also, the user has no indication of what playlist he/she is currently listening to.

The second issue is closely related to #53. Perhaps making history redirect to the playlist url for reddit, genre and other playlists would be a better solution?