Issue #3260653 by khiminrm, inversed: Allow pre-submit AJAX validation control by element or form class

Issue #3260653 by khiminrm, inversed: Allow pre-submit AJAX validation control by element or form class

• Issue #3260653: Validation of ajax forms with class 'cv-validate-before-ajax' doesn't work
• Updates the JavaScript check to look for the class in either the form or the element
• Updates the help text on the settings page to reflect how this works

Closes #3260653