Feature/add herokuish support

Added support for running at dokku (Heroku-like paas), also briefly tested that still runs locally too.

Backward incompatible changes:
- config.cfg sections and keys changed (see updated config.cfg.sample)
  - One section only (SteamDissector)
  - Keys are case-insensitive
- MongoDB connection config (now mongo_uri @ config.cfg) must include /db_name

Othewise should work as before.

Other changes:
- Configs are sourced now from (later gets priority):
  - defaults
  - config.cfg (port, mongo_uri)
  - environment variables (PORT, MONGO_URI)