[WIP] Refactor rdf type factory to accept a list of mappers per type name

This is needed by https://github.com/symfony-cmf/cmf-sandbox/pull/143 and https://github.com/symfony-cmf/CreateBundle/pull/24 to allow to use a custom RdfTypeFactory and DoctrinePhpcrOdmMapper for the route documents. Before this, a new class document (CmfRoute) was needed just to get and set locale values. 

I will do some cleaning and ask for the merge then... 

CC @dbu