Bug 15980: Use Font Awesome icons in subscription frequency deletion confirmation...

Bug 15980: Use Font Awesome icons in subscription frequency deletion confirmation dialog

If you try to delete a subscription frequency which is in use by an
existing subscription you will be shown a confirmation dialog. This
dialog should use Font Awesome icons.

Other minor changes:

- Added "action" attributes to <form>s to fix validation errors.
- Added "alert" class to confirmation dialog so that it is correctly
  styled.

To test, apply the patch and go to Serials -> Frequencies.

- Click "Delete" on a frequency which is in use by a subscription.
- Verify that the confirmation dialog is styled correctly.
- Test that the "No, do not delete" button works correctly.
- Test that the "Yes, delete" button deletes the correct frequency.

Signed-off-by: Hector Castro <hector.hecaxmmx@gmail.com>
Works as advertised

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