Support WAI-ARIA's role="presentation" inside of WikiText.

- role="presentation" is the standard way to mark some element as presentational for assistive technologies, etc...
  Such as presentational tables. Something we have a lot of and need the ability to mark as presentational.
- Other ARIA roles need more thought so for now they are not supported.

Change-Id: I426ea04a8bc48181a71a308753525f3964201748
Merge "Support WAI-ARIA's role="presentation" inside of WikiText."