fix(SEO): change h1 behavior

-- headline h1 is can now have another title than page title
(use h1: '<headline title>' in document metadata)
-- changed document generation so that only 1 h1 is currently in page
-- all h2 get same style as h1 (see h1 class in style.css)

Closes: #CAM-1437, #CAM-1438
Merge branch 'master' into live