[WIP] Refactoring to use container

This PR introduces dependency injection, fixing #35.and tidying up the mess of helpers.

Todo:

- [x] Behat tests should pass
- [x] PHPUnit tests should pass
- [x] PHPSpec tests should pass
- [x] Test embedded application -- write tests for it
- [x] QusetionHelper is not a drop-in-replacement for DialogHelper. Either force minimum Symfony version to be 2.6 or add a fallback.
- [x] Run code fixer