add multivariate test page

- add multivariate test page
- add seo body class to all seo pages
- add stylesheet for seo pages
- fix responsive issue with bottom cta button on seo pages
- fix uncaught merge conflict in multivariate-vs-ab test page
- fix center alignment of footer name li's on various pages.  I fixed this then saw an issue from Amanda on the subject https://github.com/optimizely/marketing-website/issues/215