LP#1099979 Provide facility to merge parts in the Monograph Parts display

A new facility is provided to make it relatively simple to merge parts that should be named the same, but are
not.  The user will check-off the parts that need to be merged, and click on the new Merge Selected Parts
control, at which point the "winner" will be selected from a pop-up.

Signed-off-by: Dan Pearl <dpearl@cwmars.org>
Signed-off-by: Rogan Hamby <rogan.hamby@gmail.com>
Signed-off-by: Ben Shum <bshum@biblio.org>