Bug 25101: Add ability to skip previewing results when batch extending due dates

Bug 25101: Add ability to skip previewing results when batch extending due dates

For sites with very large amounts of due dates to extend ( tens of thousands ), it can take a very long time of the results to load ( if at all ). It would be good to have a way to bypass the confirmation screen, instead directly updating the due dates before displaying the results.

Test Plan:
1) Apply this patch
2) Browse to tools/batch_extend_due_dates.pl
3) Note the new "Preview results" checkbox
4) Submit form with the checkbox unchecked, due dates should be updated
   without previewing the checkouts
5) Submit form with the checkbox checked, tool should function as
   it did previously

Signed-off-by: Kelly McElligott <kelly@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Bug 25101: (QA follow-up) Add hint to new option

Adds a hint about the large numbers behind the new
checkbox option.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Bug 25101: (QA follow-up) Fix hint for new option

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>