Check for bib_source.can_have_copies in cataloging.

Check for bib_source.can_have_copies in cataloging.

Retrieve the BRE and CBS object in the add_volumes method of
opac.js.

Check if the CBS can have copies, and if not, tell the user such
and return.

Also required adding an api entry in constants.js and a new message
in offline.properties.

This is the beginning of the client code changes. There are very
likely to be more.

Signed-off-by: Jason Stephenson <jstephenson@mvlc.org>