Modernise Yowsup

This is a WIP umbrella pull request that I will be merging individual PRs into. Please don:'t review this, but rather these:
- https://github.com/michaeljoseph/yowsup/pull/1
- https://github.com/michaeljoseph/yowsup/pull/2

When I'm done I'll ping this issue for review.

cool
michael