This changes the behavior of --items

This changes the behavior of --items

And adds an option for --exclude-itemless-bibs.  Previously, bib records without
items would not be exported at all with the --items argument.  Now they will (*),
but the --exclude-itemless-bibs argument will restore the original behavior.

* - This change was accomplished by performing a LEFT JOIN against the call number
and copy tables, but if the --library option is used, then the original vanilla
JOIN is still used, so whether an itemless bib will export or not with that
argument will depend on whether there is a non-deleted call number on the bib.

Signed-off-by: Jason Etheridge <jason@esilibrary.com>