Bug 34668: Add popup warn librarians of waiting holds when checking out

Bug 34668: Add popup warn librarians of waiting holds when checking out

When there are holds waiting for patrons, sometimes the librarian misses
the "Holds waiting here" display. This patch adds a modal popup warning
when checking out an item for a patron with waiting holds.

Test plan:
1) find a user (user1)
2) find a biblio (biblio1)
3) add a hold for biblio1 to user1
   (search biblio1 > Holds > find user1 > Place hold)
4) checkout biblio1 to another user if not already checked out
   and checkin through circulation page (not through the user page)
   > confirm hold
5) there should be a "Holds waiting here (1)" section added on user1 page

6) checkout any items that isn't the one on hold for user1
   -> notice it just checks out as normal
7) apply patch and update database
8) go to administration > system preferences > switch "WaitingNotifyAtCheckout" to "Notify"
9) refresh page and redo step 6
   -> notice there is now a modal to warn the librarian of a waiting hold
   click Ok to proceed with the checkout, click outside the modal to not do anything
10) additionnally, the popup shouldn't appear if we checkout any of
    user1's waiting hold

Signed-off-by: Matt Blenkinsop <matt.blenkinsop@ptfs-europe.com>
Signed-off-by: Mia Kujala <mia.kujala@xamk.fi>
Signed-off-by: Kelly <kelly@bywatersolutions.com>
Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>