Refactor EntityToIdentifier stuff into ObjectToIdentifier
Remove hardcoded dependency on Doctrine ORM, and allow instead to register transformer for every persistence type (ORM, ODM, PHP-CR).
Migrating LiipCacheBundle to stable version of DoctrineCacheBundle
Merge pull request #1256 from stloyd/feature/form_object_transformer

Refactor EntityToIdentifier stuff into ObjectToIdentifier