Poc/apiimport2.0

Options price computing is not finished (it's the old one). See more : https://akeneo.atlassian.net/browse/MC-35
I really don't like the naming, but I didn't found a better one. Helpers are kind of tools. One to compute configurable price changes and another one is a normalizer which not implements a Normalizer interface ( to normalize VariantGroup). If you find a better naming tell me ;)