Get rid of data_access.js, at long last. Existing calls to
Zotero.getCollections() will need to be replaced with
Zotero.Collections.getByLibrary() or .getByParent().
Also removes Zotero.Collection::getCollections(), which is redundant
with Zotero.Collections.getByLibrary(), and Zotero.Collections.add().
The latter didn't didn't include a libraryID anyway, so code might as
well just use 'new Zotero.Collection' instead.
