Collapse plugin improved accessibility using aria roles and states / keyboard listeners

Created by: bassettsj

Again from the paypal/bootstrap-accessibility-plugin, these changes should be added to the documentation and the JS plugin.

Collapse

1. Add tab role, aria-selected, aria-expanded, aria-controls, and tabIndex for collapse tab.
2. Add ARIA roles of tabPanel, tabIndex, aria-hidden, and aria-labelledBy for collapsible panel.
3. Add role of tabList and aria-multiselectable for collapse container div.
4. Dynamically flip tabIndex, aria-selected, and aria-expanded for tab when it is activated and add aria-hidden to hide the previously visible collapse tabpanel.
5. Add keydown event listener for the collapse component to work with keyboard.