PIM-3443: Fix prices export and add spec
Merge branch 'PIM-3443-2' into PIM-3443-merge

Conflicts:
	CHANGELOG.md
	spec/Pim/Bundle/TransformBundle/Normalizer/Flat/ProductNormalizerSpec.php
PIM-3443: Fix following the merge
Merge pull request #1856 from akeneo/PIM-3443-merge

PIM-3443 : merge from 1.2