Bug 11767 - Use validation plugin when creating new authority framework tag

Bug 11767 - Use validation plugin when creating new authority framework tag

The page for adding a new tag to an authority 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 out of the script and into the
template where it belongs.

To test, apply the patch and go to Administration -> Authority types ->
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>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>