Bug 11789 - Use validation plugin when creating new list

The page for adding a new list 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.

Other edits: Minor validation fixes.

To test, apply the patch and go to Lists -> New list. Try submitting the
form without entering a list name. This should trigger a validation
warning.

Submission of the form with valid data should work correctly. Editing an
existing list 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>