Use of HTML5 required attribute instead of aria-required and aria-invalid

By using the HTML5 required attribute instead of the aria-required, the browser and screenreader can immidately detect if an input is invalid instead of relying on a postback to apply the aria-invalid attribute.

Note:

• this will not be backported (IE11 support is unknown)

• it may be that the behavior of the HTML5 required attribute makes implementation of this task unfeasable due to usability concerns for regular users. Tooltips may be getting displayed for fields that are required, upsetting the usage concepts. Requires research.

• This requires changing the null-value strng from "==null==" to a blank string. This change has already been okay'ed in and