Collapse accessibility

This addresses a decent amount of issue #13555.

- Added tabIndex aria attribute to collapse plugin
- Added tab-role, aria-selected, and aria-controls into the collapse html docs.
- Added support for toggling aria-expanded, aria-selected, and aria-hidden via the javascript collapse events.

A decent amount of the changes were inspired by the example at http://accessibility.athena-ict.com/aria/examples/tabpanel2.shtml
Whoops, must have unfixed it while rebasing.