bug 2157: add ability to 'clean' staged record batches

bug 2157: add ability to 'clean' staged record batches

batches, it is now possible to 'clean' a batch by
removing all bib and item records staged in the batch.  This
has the effect of helping to reduce database space used
by old import batches as well as removing staged records
from the cataloging reservoir search.  Note that 'cleaning'
a batch affects only the copies of the records that were staged;
if the batch was committed, cleaning the batch does not
affect any bibs and items that were committed into the catalog.

Also note that once you clean a committed batch of records, it is
impossible to undo the previous commit operation.

Signed-off-by: Galen Charlton <gmcharlt@gmail.com>
Signed-off-by: Henri-Damien LAURENT <henridamien.laurent@biblibre.com>