webstaff: add another option for choosing volume transfer library

webstaff: add another option for choosing volume transfer library

The actions menu on the holdings view now has two ways of
specifying a library to transfer volumes to:

 * Library as Volume Transfer Destination

   Pops up a modal with a library selector.

 * Library from Selection as Volume Transfer Destination

   Uses the currently selected volume's owning
   library to specify the target library.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Signed-off-by: Kathy Lussier <klussier@masslnc.org>