Remove <hgroup> tag - it's out of the HTML5 spec (again!)

git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5478 2fea6a4d-a838-0410-917b-93a53c48e9d2
Change body id selector to class selector in front-side theme

git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5479 2fea6a4d-a838-0410-917b-93a53c48e9d2