Initial commit for the new extractors module

I had some free time and have worked on #846 
I have created a module named extractors where all the extractors should be moved.
Adding extractors will only require to add its name to the `extractor_names` list in `extractors/__init__.py`.
I have added some fake files and a `test_extractor_module.py` scrip to see the behaviour.
Of course if you find this OK, I will rebase the commit without these test files.