Folded the functionality from DBWriter into DocumentImpl, continuing the
work started earlir to create a more DOM-like model for the classes, in
which a single DocumentImpl class handles both reading and writing of
documents to the database. Modified shell scripts and MetaCatServlet to
reflect these changes, and removed DBWriter.java.
Work still needs to be done on simplifying the algorith by which a Document
is created, which is currently convoluted. Will check that work in soon.