Bug 11788 - Use validation plugin when creating new course

Bug 11788 - Use validation plugin when creating new course

The page for adding a new course 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.

To test, apply the patch and go to Course reserves -> New course. Try
submitting the form without entering a department, course number,
and/or course name. This should trigger validation warnings.

Submission of the form with valid data should work correctly. Editing an
existing course 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>
(cherry picked from commit 4e9b5110d90c3ac60c61f710ff5892b9720e643e)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>