Suspension of holds

Users should be able to place a hold 'on suspension'.  This means the hold will
preserve it's place in the queue, but it will be skipped over to the next
non-suspended hold when the item becomes available.  Upon un-suspension, the
hold will resume it's original place in the queue.

There shall be a button to suspend all holds for a user at once, both in the
staff client and the OPAC (if OPAC holds management is enabled)

Auto unsuspend holds by date

For users who know the date when they will be able to receive holds again,
there shall be an available box to specify this date at suspension time.  When
that date rolls around, the hold will be automatically resumed.  This box shall
also be available when suspending multiple holds at once.  This box shall be
available in the staff client, and in the OPAC (if OPAC holds management is
enabled).

The use of this features shall be toggleable by a system preference.