Add worker runner (hypothesis-worker)

[nickstenning]

Add a console script called hypothesis-worker, which can be used to run worker functions from the command line. Worker functions are registered under the h.worker entrypoint.

[tilgovi]

Merging. Only thing I changed is BASE_URL to APP_URL. I plan to install https://github.com/mikecsh/dokku-app-url. That will make things Just Work (tm) for all but prod (since we vhost it with no subdomain).