Add real-time statistics hub

[Protohedgehog]

Find a way to integrate this https://github.com/lhehnke/opensciencemooc-followers from @lhehnke as a blog post.

Either as :

• [x] a single static page
• [ ] something that regularly updates on the site.
  • [ ] github commits and stars
  • [ ] twitter followers, likes and retweet
  • [ ] eliademy

cc @dannycolin @tosteiner