Bug 27668: Improve validation of patron entry form in the OPAC

Bug 27668: Improve validation of patron entry form in the OPAC

This patch improves the way we handle required fields in the patron
entry/update form in the OPAC. Instead of doing multiple checks for each
field using mandatory.defined(), the template now loops over a list of
fields and sets a "required" variable for any which are required.

Then, for each form field, the "required" variable is used to set
classes on labels, input fields, and the "required" text hints. The
class on form fields acts as a hook for the jQuery validator plugin. The
class on the text hints allows us to hide the text hint using CSS,
eliminating the necessity of using a template conditional.

The patch also adds the missing validator-strings include which enables
translation of the jQuery validator plugin's validation error messages.

To test, apply the patch and rebuild the OPAC CSS
(https://wiki.koha-community.org/wiki/Working_with_SCSS_in_the_OPAC_and_staff_client).

 - Go to Administration -> System preferences and enable
   PatronSelfRegistration.
 - Select multiple fields to be required using the
   PatronSelfRegistrationBorrowerMandatoryField preference.
 - In the OPAC, start the process of registering for an account.
 - The fields you designated as mandatory should each have a "Required"
   label under them.
 - Try to submit the form without entering any data. The required fields
   should now be highlighted in red and have another label, "This field
   is  required."
 - Fill in the required fields and submit the form. It should submit
   correctly.
 - Modify the PatronSelfRegistrationBorrowerMandatoryField preference
   and select all fields as mandatory. Confirm that all fields in the
   patron entry form work correctly.
 - Test that form validation works correctly when modifying a logged-in
   patron's existing account.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>