Document Metadata (Errors and Title)

** Document Metadata (Errors and Title) **

This PR adds two fixes to the metadata template for documents.  It replicates the layer metadata template where possible.  First, it creates a title for the "Editing details for ____", since documents do not have a typename.  Second, it replicates the error display from the metadata template for layers.  Categories are "required".  Therefore, metadata updates were previously failing silently without any errors displayed if the user did not select a category.

Additional fixes coming soon that will affect layers, documents, and maps together.
formatting - run pep8 or something
this can also be simplified to:
`return '%s (%s)' % (self.title, self.id)`