PIM-3101 : introduce a product value normalizer
PIM-3101 : update product normalizer spec
PIM-3101 : add a spec for flat product value normalizer
PIM-3101 : update specs to deal with array and collection normalization
PIM-3101 : remove deprecated unit test (has been replaced by specs)
PIM-3101 : cleanup
Merge pull request #1389 from akeneo/PIM-3101-flat-product-value-normalizer

PIM-3101 : introduce a flat product value normalizer