Bug 29346: Circulation actions triggers

Bug 29346: Circulation actions triggers

This patch introduces triggers for real-time updating the holds queue at
check out and check in.

The following high-level methods are involved:

- C4::Circulation::AddIssue
- C4::Circulation::AddReturn

To test:
1. Apply this patch
2. Run:
   $ kshell
  k$ prove t/db_dependent/Circulation_holdsqueue.t
=> SUCCESS: Tests pass! Triggers are triggered
3. Sign off :-D

Note: I put the tests on a separate file because the other one was too
big already.

Sponsored-by: Montgomery County Public Libraries
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>