* Moves the choice-label <input> elements inside of their <label> tags.
* Wraps long-answer and slider question text in a <label> tag.
* Uses <th> instead of <td> elements inside <thead>, for the instructor tool and plot preview tables.
* Links the feedback, and choice-tip text with the choice labels via aria-describedby.
* Wraps the choice-result feedback icons inside the label elements, to match CAPA a11y design.
* Adds translated, aria-visible labels for the "correct answer/choice" checkmark and "incorrect answer/choice" X.
* Adds the 'aria-live="polite"' attribute to the divs whose content changes dynamically.
* Removes block-level children from <legend>, placing the h3.question-title outside the <fieldset>.
* Fixes tests broken by above commits
* Adds tests for new aria-label attributes..
