Fixes memory leak on generic Doctrine Writer

The writer uses now the ProductCacheClearer
Merge branch '1.2' into fix/PIM-3121

Conflicts:
	CHANGELOG.md
Merge branch 'master' into fix/PIM-3121

Conflicts:
	CHANGELOG.md
Merge pull request #1433 from akeneo/fix/PIM-3121

Fixes memory leak on generic Doctrine Writer
Fixes CHANGELOG
Set version number
Merge branch '1.2'
Fixed writer bugging with attribute group import
Merge branch '1.2' of git://github.com/akeneo/pim-community-dev into 1.2
Fixed bug with updating of associations
Fixed print_r of entities causing out of memory errors
Add missing queries in upgrade doc
Add missing queries in upgrade doc
Revert "Fixed bug with updating of associations"

This reverts commit 135f0b5e74a5bf51ebd43a8aa326ecd4a31602fd.
Revert "Fixed writer bugging with attribute group import"

This reverts commit 263717e8b64abef60f73199a3f0f90525bab0fa8.
Fixed bug with updating of associations
Corrected association import failing if owner not found
Fixed bug in MongoDB association normalizer when association members did not have a MongoDB Id
Added missing property
Fixed writer bugging with attribute group import