Added Windows Phone 8 Support

Built against GWT 2.6 RC3 but should be fine with GWT 2.6 final

I did not find a way to get showcase to work across all permutations unless I added to the showcase index.html file meta name="viewport" content="width=device-width". WP8 needs this setting and other permutations continue to work fine.

I could not find a way of dynamically adding the meta viewport tag or @-ms-viewport css style so that IE10 mobile on WP8 would pick up the correct viewport settings

IE desktop exhibits a strange behaviour where sometimes it will disappear behind another window when you first start to move around the application. Simply do not have any other windows opened when in IE10 desktop. This will need investigating at some point.