Custom Prompt class based on the HTML5  "data-required-class" attribute.

I was doing a project where I needed multi-tiered required fields. So "red" was for primary then I made more classes for "secondary / tertiary" etc. So that when the whole form was validated, the "required" alerts were all different depending on the class defined in the "data-required-class" attribute. Thought
it might be useful to others as well. 

Also added in support for prettySelect.