Bug 17183: Check if any checkboxes have been checked for 'Delete Selected' button...

Bug 17183: Check if any checkboxes have been checked for 'Delete Selected' button in Koha News

To test:
1) Go to Tools -> Koha News
2) Click 'Delete selected' button without selecting anything
3) Notice you are asked to confirm if you would like to delete ... but
you didn't choose anything to delete
4) Apply patch and refresh page
5) Click 'Delete selected' button without selecting anything
6) Should see alert.
7) Select one or more news items to delete and click 'Delete selected'
button
8) Should be asked to confirm
9) Confirm that the delete works as expected

Sponsored-by: Catalyst IT
Signed-off-by: Claire Gravely <claire_gravely@hotmail.com>
Signed-off-by: Katrin Fischer  <katrin.fischer@bsz-bw.de>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>