Add alt text and role to figure

The figure and figcaption elements are not currently accessibility supported by the majority of browsers. Until the figure and figcaption elements are widely accessibility supported by browsers and/or assistive technology it is recommended that role="group" be used on the figure element and in the case where the figcaption content is the text alternative, provide a label for the image in the alt attribute.
See: http://www.w3.org/TR/html-alt-techniques/#m6