(#1574) - Website icons

This adds Twitter, CouchDB & Github Icons to the footer, I think we should add the more devops ones into the README.md. So Travis badge, and Saucelabs Matrix badge.
Also in order to get them to display nicely I've added better structure on smaller screens.
Also fixes https://github.com/pouchdb/pouchdb/issues/1928
![](http://i.imgur.com/r4LKULB.gif)