Tags

Stuff that needs to be updated:

• Don't use site/search for getting related pages (our data model supports getting that data in an efficient manner)
• Add tag clouds
• Change UI to add a tag at a time, so we can autocomplete
• Add the user: prefix, which allows a user to be notified of a page
• Support date-range inside API (so we don't need to be doing DB selects from the front-end)