Bug 33817: Prevent item bundle that is checked out to be modified

Bug 33817: Prevent item bundle that is checked out to be modified

While an item bundle is checked out, we don't want any items to be
added or removed from the bundle.

To test:
* Create a record with LDR Pos. 7 = c
* Add an item for your bundle
* Add one or more existing items from other records to the bundle
* Check out the bundle item
* Verify it appears correctly on the patron account
* Verify you can still add/remove items from the bundle
* Apply patch set
* Verify that the add/remove links are now disabled (greyed out)

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>