Bug 7131: teach MARC import how to overlay items

Bug 7131: teach MARC import how to overlay items

When staging biblios with items attached you previously had only two
options, add or don't add.

This patch adds a third option to replace an item record if a match is
found on itemnumber or barcode, else it adds the item.

Test Plan:
1) Stage a file of biblios with items attached.
2) Import the batch into the catalog.
3) Run the indexer so the matcher will match
4) Modify the item data for at least one bib in the file
5) Re-stage the file with the item matching option set to "Replace
   items if matching bib was found"
6) Let the indexer run again
7) You should see updated item information after the overlay

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Henry Bankhead <hbankhead@losgatosca.gov>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>