Bug 5790 - Prevent deletion of records with holds

Bug 5790 - Prevent deletion of records with holds

Test Plan:
1) Apply patch
2) Create a record
3) Create an item for the record
3) Place a hold on the bib
4) Attempt to 'Delete all items', you should recieve
   an error message stating to delete all holds before
   deleting all items.

Also, it is possible to get into a situation where a record has
holds but no items. In this situation, it is not possible to
view/delete the holds without adding an item back to the record.
In this case, attempting to delete the bib causes a warning, but
does not prevent deletion.

Signed-off-by: Liz Rea <liz@catalyst.net.nz>
Passes tests - do note that it was a design decision to leave the delete links clickable even though they are grey.
The reasoning is that librarians will want to be able to know *why* they cannot delete a given item or bib - I like this.

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>