placing multiple holds: indicate number of holds that can be placed

[Galen Charlton]

When a user places multiple holds on a title or metarecord (see bug 1694058), it would be nice if the request form adjusted the copy count selector to reflect the number of holds that the user can place, rather than the limit.

For example, suppose that the duplicate hold limit is set to 25. Further suppose that a user has placed 20 holds on a title for their book club, then decides to add two more hold requests. When they go to the place hold form, it would be nice if the drop-down went up to 5, not 25.

Evergreen master