LP#1838995: Hold subscription buckets

LP#1838995: Hold subscription buckets

This feature allows staff to add multiple users to a named hold subscription
bucket and place title-level holds for a record for that entire set of users.
Users can be added to such a hold subscription bucket from either the patron
search result interface, via the Add to Bucket dropdown, or through a dedicated
Hold Subscription interface available from the Circulation menu.  Adding new
patrons to a subscription bucket will require staff have the PLACE_HOLD
permission.

Holds can be placed for the users in a subscription bucket either directly from
the normal staff-place hold interface in the embedded OPAC, or by supplying the
record ID within the subscription bucket interface.  In the latter case, the
list of users for which a hold was attempted but failed to be placed can be
downloaded by staff in order to address any placement issues.  Placing a
subscription bucket hold will requires staff have the MANAGE_BATCH_HOLDS
permission, which is new with this development.

In the event of a mistaken subscription hold, staff with the MANAGE_BATCH_HOLDS
permission will have the ability to cancel all unfulfilled holds created as
part of a subscription hold event.

A link to the title's hold interface is available from the list of subscription
hold events in the dedicated subscription hold interface.

Signed-off-by: Mike Rylander <mrylander@gmail.com>