List widget now implement the WIA ARIA 1.0 Grid pattern

List widget now implement the WIA ARIA Grid pattern defined in http://www.w3.org/TR/2013/WD-wai-aria-practices-20130307/#grid

This version solves issue https://github.com/ibm-js/deliteful/issues/55
(default renderer labels should not be separately focusable).

This version also allows using actionable HTML inputs in items renderer
(see the list samples).