Set process name for long-running processes

For long-running processes it can be convenient to have a short and
human-readable process name. For example, in our typical server
configuration we have quite a few Mutalyzer processes running with very
long process names, making ps and top output hard to parse.

It is assumed that in production environments the webservices and
website are ran in a separate WSGI server such as Gunicorn which can be
configured to set the process name.

The setproctitle dependency for this feature is a C extension and we
therefore make it a soft dependency. Construction copied from Gunicorn:

https://github.com/benoitc/gunicorn/blob/5bc13be79ecaf8f1027764c600023f674ebcf5b2/gunicorn/util.py#L55