adding support for phpcr

I wanted support for the phpcr within the FOSElasticaBundle so I wrote this prototype of phpcr support. 

I think it's not complete yet but i would love to get some feedback on this, to know whats missing or what may fail. At the moment I think at least a custom provider class is missing, I'm working on that now.

@dbu would love to see your feedback here.

Also FriendsOfSymfony/FOSElasticaBundle#729 may be in conflict with this and should get merged in frist place.