Ispn 3150/accept for bytearrays

This PR should be merged after https://github.com/infinispan/infinispan/pull/1876

* Now the x-java-serialized-object type is not chosen by accident (prviously it was chosen regardless of users choosing application/x-java-serializable-object or application/my-extra-super-trooper-non-existent-type)
* Byte arrays are only returned as octet-stream - no other option (if users store byte arrays, they probably expect byte arrays to be returned, not x-java-serializable-object; the x-java-serializable-object can still be returned for Serializable objects)
* Be stricter when users define incorrect Accept for serializable objects - previously, any nonsense value being specified by a user lead to x-java-serializable-object being returned. Now the BAD REQUEST is returned instead