Bug 11771 - Use validation plugin when creating new MARC framework tag

Bug 11771 - Use validation plugin when creating new MARC framework tag

The page for adding a new tag to a MARC framework includes some
custom form validation JavaScript which can be removed in favor of HTML5
validation attributes and Koha's built-in validation plugin. This patch
does so.

The patch also moves some tag markup creation out of the script and into
the template where it belongs.

To test, apply the patch and go to Administration -> MARC bibliographic
framework -> MARC structure -> New tag. Try submitting the form without
entering a tag number. This should trigger a validation warning.

Submission of the form with valid data should work correctly. Editing an
existing tag should also work correctly.

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Great improvement! Before this patch, I got a JS alert but the form was
submitted anyway.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit d90b4b6a08aa946fd40d1c1a45d1cc4ad64c30e5)