DDC-391: Add support to configure custom persister classes

Based on https://github.com/doctrine/doctrine2/commit/8c3ad50bb5ad51f9064543768745f3d85f4b7d64 (from the http://github.com/doctrine/doctrine2/tree/OverridePersisters branch)

Basis for feature: http://www.doctrine-project.org/jira/browse/DDC-391