Bug 27864: Visual feedback on overridden pickup locations when placing hold

Bug 27864: Visual feedback on overridden pickup locations when placing hold

This patch makes the form for placing a hold, use the API to retrieve
the valid pickup locations for a biblio.

To test:
1 - In Circulation and fines rules > Default checkout, hold and return policy, change 'Hold pickup library match' to 'item's home library'
2 - Set AllowHoldPolicyOverride system preference to Allow
3 - Try placing a hold on a biblio with several items.
    Ensure that there is one item with homebranch of the patrons branch and
    one at another branch
4 - Note the pickup location dropdown lists all branches, even those not matching the policy (Item's home library)
5 - FAIL: There's no sign they are overrides to rules
6 - Apply the patch
7 - Repeat 3
8 - SUCCESS: Same behavior as before all libraires listed, but there's a sign
    + tooltip for overridden ones.
9 - Sign off :-D

Note: styling follow-up coming

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>