Refactor worker for dependency injection

[dinoboff]

• refactor for dependency injection: expect for the helpers (like lodash.*) and request, there's no need to monkey patch imported modules.
• get 100% coverage of src/*.js
• implement pivotal expert service handler: I am assuming the worker can get anonymous access to pivotal expert firebase app for some public data; We just a regular client apiKey and the path to the achievement to fetch.
• add more debug message.
• add back code school service handler.
• add some kind of e2e test for index.js.