Bug 15979 - Use Font Awesome icons subscription deletion confirmation dialog

 Bug 15979 - Use Font Awesome icons subscription deletion confirmation dialog

When deleting a subscription which has not expired or which has linked
issues or items, a dialog asks for confirmation. This patch updates the
dialog to use Font Awesome icons.

Other minor change: Corrected capitalization in dialog heading.

To test, apply the patch and go to Serials.

- Locate a subscription which can be deleted and which has not expired,
  has linked items, or has linked issues.
- View the detail page for that subscription.
- Choose "Delete subscription" from the "Edit" menu.
- Verify that the confirmation dialog is correctly styled.
- Verify that the "No, don't delete" button works correctly.
- Verify that the "Yes, delete" button deletes the subscription.

Signed-off-by: Nicole C Engard <nengard@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>