Added an option to normalize other content types

The normalizer is only applied when the data is decoded which is not the case with `multipart/form-data`.

Fix issue https://github.com/FriendsOfSymfony/FOSRestBundle/issues/868.
We used the setter to configure the optional `arrayNormalizer` property but since we now need an other optional dependency, I thought it was messy to have two setters so I moved it to the constructor with a default value instead.