Comment 6 for bug 1998605

Here's a branch for testing that takes the approach of not allowing checked out items to be marked missing: https://git.evergreen-ils.org/?p=working/Evergreen.git;a=shortlog;h=refs/heads/user/dbriem/lp1998605_prevent_mark_missing_when_checked_out

I think items can be marked missing from:
- patron items out
- patron holds
- catalog record holdings tab (already blocks checked out items from being marked missing)
- pull list
- hold shelf
- item status (detail and list views)

This removes the option from the items out grids, open-ils.circ.mark_item_missing no longer allows a checkin attempt if the item's checked out, and (since attempts may error out more often now) the AngularJS circ service tries to keep the promise chain alive when marking multiple items missing (this is consistent with the Angular behavior).