Update FileHandler

* Added step to filter for *.test files to handle2Args.
* All tests of FileHandlerSpec pass.
Update FileHandler, StepProcessor and tests

* FileHandler functions are private again.
* Edit handle2Args to make it more readable.
* Edit FileHandlerSpec for better path names.
* Created stub in StepProcessor to write tests against.
* Implemented StepProcessor test for the scenario when processSourceFile is called with only 1 test-case and a map.