Bookmarks use old spec

The current implementation for fetching bookmarks relies on [the outdated XEP-0048 version 1.0](http://www.xmpp.org/extensions/attic/xep-0048-1.0.html) (which in turn uses [XEP-0049: XML Private Storage](http://xmpp.org/extensions/xep-0049.html) rather than [the latest XEP-0048 v1.1](http://www.xmpp.org/extensions/xep-0048.html) which uses [XEP-0060: PubSub](http://xmpp.org/extensions/xep-0060.html) via [XEP-0223: Persistent Storage of Private Data via PubSub](http://xmpp.org/extensions/xep-0223.html).

This is a problem in itself, since other clients using the newer specs will produce bookmarks that we simply ignore. Additionally, I intend to implement the other side of bookmarking in Candy, and this is tricky with the old method since it appears not to allow piecemeal addition of bookmarks, instead requiring writing the whole set every time (if I am wrong here, I'd love someone to correct me).

I will add this support in parallel such that both sources of bookmarks are checked.