default permissions setting in ddr.cfg, settings

Default values for the 'public' field for collections, entities,
and files.  We're going with 'public=1' by default.
include file 'public' field in entity files listing

We need to be able to remove non-public files from repository.
The Git repo tools available only allow the removal of complete
files.  Entities keep records of the files they contain.
We don't want to have bad links.
So, add files' public field value to entity.json.
add public field to colls,entities; add dropdown,default to files

Collections and entities previously did not have a public field.
Files had one but it wasn't a nice drop-down menu and was not
connected to the new default perm setting.
show file.status and file.public on detail page