Backport PR #6249: always use HTTPS getting mathjax from CDN

Is there any reason not to do this now?

closes #6246
Backport PR #6279: minor updates to release scripts

- unicode fixes in github_stats
- remove unused Windows and egg bits
- update Python 3 builder to 3.4
Backport PR #6273: Upgrade default mathjax version.

This also fixes an issue with ```from IPython.external import mathjax; mathjax.install_mathjax()``` not working properly, because of a changed version schema.
release 2.2.0
Merge tag 'rel-2.2.0' into 2.x-backports

release 2.2.0