Bug 26201: Remove the use of jquery.checkboxes plugin from batch extend due dates...

Bug 26201: Remove the use of jquery.checkboxes plugin from batch extend due dates page

This patch removes the use of the jquery.checkboxes plugin from the
batch extend due dates page.

Unrelated change: Removed 'enctype="multipart/form-data"' from the form
because there is no file upload.

To test, apply the patch and go to Tools -> Batch extend due dates.

 - Submit the form with parameters which will return a set of multiple
   checkouts.
 - On the results page, test the "Select all" and "Clear all" links to
   confirm that they work correctly.

Signed-off-by: Amit Gupta <amit.gupta@informaticsglobal.com>

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>

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