Collapse accessability

 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.

 References issue #13555

 Sweet example at
 http://accessibility.athena-ict.com/aria/examples/tabpanel2.shtml