Use PropertyAccess for extend usability of getFieldValue

Current implementation is a bit too light (getter/isser) when PropertyAccess already used elsewhere in this bundle offer more (hasser/magic function)
This allow bundles like A2lixI18nDoctrine Bundle and KnpLabsDoctrineBehaviors which allow a __call method as proxy method to work with ease with Sonata.

See http://a2lix.fr/blog/2014/08/04/translate-internationalize-doctrine-entities-sonata.html

Any thoughts?
is the Accessor can pass the $paramters options ? if not it is a BC break