Add support for <input type="week"/>

This is to add support for the week input type. This follows the HTML5 spec which specifies using ISO-8601 standards for identifying dates. As such, the date output to the model is the Thursday of the week. Per ISO-8601, the "first week" of the year is whatever week has the first Thursday of the year.

Also added output for week-of-the-year to `$filter('date')`. This allows the date of the year to be output as follows:

     var value = new Date(2013, 0, 12); // Jan 12, 2013
     console.log($filter('date')(value, 'yyyy-Www'); // 2013-W01