Add missing setproctitle dependency

It’s required by shoebill, yet not included in setup.py’s requirements list.

On a side note:

```
Downloading/unpacking GitPython>=0.3.1 (from shoebill==0.1)
  Could not find a version that satisfies the requirement GitPython>=0.3.1 (from shoebill==0.1) (from versions: 0.1.7, 0.2.0-beta1, 0.3.0-beta1, 0.3.0-beta2, 0.3.1-beta2, 0.3.2.RC1)
```