Incremental fix for Bug 3514, Returning items through patron details tab

Incremental fix for Bug 3514, Returning items through patron details tab

Note: Signed off with the understanding that this partial fix still doesn't compensate for items that need to be transited home (i.e. have no holds, but are not being returned at their home branch.)
 This behavior is much better than the old behavior, however.

Hiding the "check in" checkbox for items which are on hold. This
mitigates the problem of checkins not triggering holds prompts
by forcing the librarian to check in these items individually.

This fix should be considered temporary until a more comprehensive
fix can be developed which incorporates handling for holds.

Signed-off-by: Liz Rea <lrea@nekls.org>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>