Using SonataClassificationBundle without SonataMediaBundle

Even if you do not want to use SonataMediaBundle, some other bundles come with (SonataAdminBundle, SonataClassificationBundle ...).

Several consequences:
 - The relationship (parent, children) are not created. Indeed, at the beginning of the test function (SonataClassificationExtension :: registerDoctrineMapping) still fails, ApplicationSonataMediaBundle does not exist.
 - As the SonataMediaBundle code is present SonataMediaBundle (dependency composer), the interface_exists function ('Sonata \ MediaBundle \ Model \ MediaInterface') always returns true.
Using SonataClassificationBundle without using SonataMediaBundle is thus not possible. 

My modification can enable or not the use of SonataMediaBundle of adding a "use_media" parameter in the configuration.