LP#1695062 - webstaff Make non-freetext required stat cats actually required

LP#1695062 - webstaff Make non-freetext required stat cats actually required

In the Patron registration form this custom drop down needed to
have an ng-class attribute with the proper
object expression in order to do add class ng-invalid if the
stat cat was required and not there.

Signed-off by: Cesar Velez <cesar.velez@equinoxinitiative.org>