Attempt to comply with twelve-factor methodology

* Move as many tunable values as possible into environment variables.
* Set some sane-ish defaults in .env.example for easy overrides
Merge pull request #2 from performanceci/feature/12factor

Attempt to comply with twelve-factor methodology
Refactor backend workers

* Split off each task to separate class
* Specs for workers and integration
* Use vegeta for http tests