Add css viewport declaration

Internet Explorer 10 in Windows 8 'snap mode' adheres to the W3C's Device Adaptation spec to allow CSS to target its viewport size. This means the existing media-queries do not work correctly. This is described in this article: http://timkadlec.com/2012/10/ie10-snap-mode-and-responsive-design/

Adding a viewport declaration ensures we adhere to the standard. Opera Mobile also supports this standard from version 11 so their vendor prefixed version is also included.

This forms part of Story number 41332915