MC-72: Add select and multiselect to attribute normalization
Merge branch '2.0' into MC-72

Conflicts:
	Helper/AttributeMappingHelper.php
	Normalizer/AttributeNormalizer.php
	Normalizer/ProductLabelDictionary.php
MC-72: Add specs
MC-72: Fix cs and doc
Merge pull request #312 from akeneo/MC-72

MC-72: Add select and multiselect to attribute normalization