Support journal abbreviations

This is a preliminary patch for journal abbreviation support. It currently only loads one abbreviation list, although it's designed to support several. The current prototype uses synchronous SQL, which I don't really like, but I don't see a way around unless we want to load the whole abbreviations list object into memory. @fbennett, would you mind having a look to see if there's anything this design lacks?

Still TODO:
1.  UI for creating/loading alternative abbreviation lists (and maybe creating abbreviation lists?)
2.  Abbreviation list selector for document preferences window (at least until we can specify an abbreviation list URI in CSL).