Bug 19401: Add confirm message when deleting invoice

Bug 19401: Add confirm message when deleting invoice

To test:
1) Go to Acquisitions
2) Go to Invoices (left nav menu)
3) Click Search (no need to filter results)
4) Click dropdown menu for an invoice, click Details
5) Click Delete
6) Notice invoice is deleted instantly
7) Apply patch and repeat steps 4 and 5
8) Confirm the confirm message shows and works as expected

Sponsored-by: Catalyst IT
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>