Apply jackmoore#765 a11y improvements (#1)

* Aria Accessibility compliance. fixes jackmoore#765

This is a formal approach to fixing jackmoore#765 with proper use of Aria
attributes as an alternative to PR jackmoore#821.

Changes include:

*  Add `aria-hidden` attributes on the dialog box and navigational
   buttons.

*  Update the `aria-hidden` value to `true` or `false` at the
   appropriate times.

*  Add `aria-label` attributes to navigational buttons, using the
   colorbox default settings at page load time, and then update the
   value when a colorbox is loaded.

*  Add `aria-labelledby` and `aria-describedby` attributes to the
   div containing `role='dialog'`.

* Pass HTML_CodeSniffer WCAG 2.0 tests

* Cleanup unneeded aria-labels, fix autoreading of dialog by using ARIA live regions and ensure focus is on the first element in the dialog when it opens

* Fix spelling of 'aria-label'

* Cleanup unneeded aria-labels, fix autoreading of dialog by using ARIA live regions and ensure focus is on the first element in the dialog when it opens

* Reworked focus trapping

* Updated minified version

Co-authored-by: James Wilson <jrwilson3@gmail.com>
Co-authored-by:  <bramd@brams-hp.localdomain>
Co-authored-by: Bram Duvigneau <bram@bramd.nl>