Generate a directory of contributors

[aalmiray]

We can harvest the github accounts from the achievement links; create a new page with alphabetical order; link it at the home page.

[madmas]

We started to work on this during Hackergarten in Dortmund: https://github.com/andreashouben/hackergarten.github.io/blob/github_scraper/src/pr-stats/prStatsScraper.js