Use Taxonomy Terms instead of Keywords

I haven't started working on the Taxonomy integration portion of the 7.x-2.x upgrade, so I'm not sure exactly how much work will need to be done here.

We want keywords stored as Drupal Taxonomy Terms instead of being stored using Biblio's old "field" system.
I've implemented a Drupal field called Keywords, but it's really just a placeholder until we can get Taxonomy integration rolling.