PIM-1568 Fixed referenced collection specs
PIM-1568 Created the "entities" ODM type
PIM-1568 Convert collection of entities to an array of identifiers
PIM-1568 Renamed ODM custom type
PIM-1568 Fixed php doc
PIM-1568 Introduced the ODM entity type
Merge branch 'master' into pim-1568

Conflicts:
	src/Pim/Bundle/CatalogBundle/Doctrine/ReferencedCollection.php
PIM-1568 Dropped ODM specs if mongo ext is not installed
PIM-1568 Spread usage of ODM custom types "entity" and "entities"
PIM-1568 Improved ODM custom type "entities" exception message
PIM-1568 Skip ODM spec when mongo ext is not loaded
Merge pull request #839 from akeneo/pim-1568

PIM-2189 Mongoize the PIM