typechecking in entity dump_json
rm entity.filemeta log field
pull file.set_path out of file.__init__

When path is set, a couple other things happen: file.src and
file.basename are set based on value of file.path.
file.make_thumbnail function stub
a mostly-working entity.add_file method; rm from views

This belongs within ddrlocal rather than in webui.
Ultimately most of the work of this method will be farmed out
to Celery but we have to get it working *at all* first.