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
take the example of a button that shows/hides a nav menu - here, the button would not need aria-selected, it would be against the spec to indicate the trigger button as "selected". in some situations aria-selected may be ok/needed (such as a classic tab navigation), but i would not generalise it into the actual plugin js here, as there are other uses/situations where it would not be appropriate