Bug 15866: Add confirm message for deleting rotating collection from toolbar

Bug 15866: Add confirm message for deleting rotating collection from toolbar

To test:
1) Go to Tools -> Rotating Collections
2) Click on any rotating collection ('Add or remove items' from drop down menu)
3) Click 'Delete' from toolbar. Validate you are now asked to confirm your deletion. Check that cancel works, then check that confirm works.

Sponsored-by: Catalyst IT
Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
I've added the word 'rotating' before collection, to make
it clear for translators what is meant here.

Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>
(cherry picked from commit a48d166bbf506287355c9fceea2633159308c530)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>