Add Accessibility/ARIA compliance to all components

[icfantv]

We need to review all the components for ARIA accessibility compliance and implement as appropriate per the ARIA spec.

Things we need to consider and evaluate:

• Keyboard Navigation for Widgets
• Keyboard Focus
• ARIA States and Properties
• Open Ajax Accessibility examples

Supported Components:

• Accordion (docs)
• Alert (docs, as modal)
• Buttons (docs)
• Carousel (docs, example)
• Collapse (docs)
• Datepicker (docs)
• Dropdown (docs)
• Modal (docs)
• Pagination ([docs])
• Popover (docs)
• Progressbar (docs)
• Rating ([docs])
• Tabs (docs)
• Timepicker (docs)
• Tooltip (docs)
• Typeahead (docs)