PIM-2113 Restored the unique axis constraint on the product
PIM-2113 Fixed mass add to group scenario
PIM-2113 Updated changelog
Merge branch 'master' into bugfix/pim-2113

Conflicts:
	CHANGELOG.md
Merge pull request #783 from akeneo/bugfix/pim-2113

PIM-2113 Restored the unique axis constraint on the product