Bug 21565: Add modal to SCO confirm

Bug 21565: Add modal to SCO confirm

This patch uses the confirmModal framework to add a modal confirm to
SCO Finish.

TO TEST:

1. Enable SCO and go to /cgi-bin/koha/sco/sco-main.pl. Make sure
   SelfCheckReceiptPrompt is set to 'show'
2. Login and click 'Finish' to see the old print alert box.
3. Apply patch and repeat steps 1 and 2.
4. Make sure the modal works for confirming and denying a receipt.
   Checkout some items and make sure everything still functions the
   same.
5. Make sure when printing a receipt that the print dialog automatally
   shows
6. Set SelfCheckReceiptPrompt to 'Don't show' and confirm behavior is
   acceptable.

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>