Memory usage optimization by not loading all pending versions

Conflicts:
	src/Pim/Bundle/VersioningBundle/Command/RefreshCommand.php
	src/Pim/Bundle/VersioningBundle/Entity/Repository/VersionRepository.php
	src/Pim/Bundle/VersioningBundle/Model/Version.php
Uses the provided getObjectManager() function
Add bug fix note on changelog
Fixes styles and version class fetching
Merge branch 'master' into fix/version_mem_leak

Conflicts:
	CHANGELOG.md
Merge pull request #1284 from akeneo/fix/version_mem_leak

Fix/version mem leak