Had some problems with PuSH and Salmon use of Bookmarks; they were
being required to generate Atom versions of the bookmark _before_ the bookmark was saved.
So, I reversed the order of how things are saved, and associate notices and bookmarks
by URI rather than notice_id.
Form for saving bookmarks that looks like the delicious.com form.
Save a new notice with the right text, but attach a new notice_bookmark
table which marks this as a bookmark. Tags, URLs are kept the same.