Allow to add serializers through config

This allow to add serializers to the SerializerAdapter plugin manager the same way as many other ZF 2 components. Basically, you can either implement SerializerProviderInterface in your module class, or adding the serializers key in your config array.

@weierophinney > Could you merge this for 2.1 plz ? Btw, in this PR I've done what I told you about previous time (moving the service listener stuff into the own manager factory). If it's ok for you I'll do this for all others plugin managers once ZF 2.1 is out.