LP#2015484: add --exclude-hidden option to marc_export

LP#2015484: add --exclude-hidden option to marc_export

This option, when used in conjunction with the various
options that export items, excludes ones that are suppressed
from the OPAC.

To test
-------
[1] Various make some items OPAC-hidden via the four
    ways that this can be done in Evergreen (i.e.,
    org_unit, item, item status, or shelving location).
[2] Apply the patch and run marc_export with
    --exclude-hidden, --items, and/or combinations of
    --library and --descendants.
[3] Verify that the hidden items are not emitted in
    the 852 fields.
[4] Also verify that bibs that have no visible items
    are also excluded.

Signed-off-by: Galen Charlton <gmc@equinoxOLI.org>