Collapse accessability

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
the various tabIndex additions are unnecessary, as a link (an <a> element with an href, as opposed to an anchor) is already focusable by default.

the use of aria-selected here is wrong per spec http://www.w3.org/TR/wai-aria/states_and_properties#aria-selected though