GIA-3216 - Fixed issue - Simple comment screen says 'comments are closed...

...' even when they are open. The nesting structure in the SASS file _container.scss of the class .comments-closed-label depended on the parent class .container__action (without it the closed comments label always appears) which was now incorrect as the closed comments label was moved from the right to the left hand side and appears under the main Comments headline with the .container__title div as parent. Also added a media query so that the Only the Post a comment icon appears in mobile view ports (up to 450px width) and the label 'Post a Comment' and the icon both appear above that viewport size as there is more space.