[WIP] 13 decoupling interface

#11 + #13 

So @rande I add the interfaces list by configuration and then I plug the admin extensions

@dbu no need to implement the base interface I use uow as you explain and you just have to configure your interface
To check if a model is translatable I have introduced a TranslatableChecker which used the interfaces list configure
I did not use isDocumentTranslatable because it's possible that a document istransable in PHPCR but it's not configure to be handle by sonata translation bundle.

What to you think about this ?

So, now I need to document this and if we want to go at the end of the concept, do the same for gedmo and check locale via doctrine mapping.