Bug 31921: Add confirmation modal when deleting a vendor

Bug 31921: Add confirmation modal when deleting a vendor

This patch adds a new modal for confirming vendor deletion. It fixes
the previous functionality, showing a confirmation modal for each
vendor and appropriately handling the response.

To test:
1) Visit Acquisitions home. Under where it says 'Manage orders', click
   the search bar to bring up the list of vendors.
2) Add a few vendors by clicking 'New' and 'Vendor'. After this, go back
   to the vendor search so that all the vendors are showing.
3) For each vendor, click on 'Delete vendor' and ensure the modal shows
   properly.
4) Attempt to delete one of the vendors. Go back to the vendor search
   and ensure they are deleted correctly.
5) Click on a vendor's name to go their supplier page. Make sure modal
   works properly and attempt to delete a vendor from here.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>