Enable Mockito mock serialization/deserialization across classloader/JVM

This pull request will enable mocks to be serialized in a certain way, that will allow them to be serialized and especially deserialized outside the classloader the mock was created.

At the moment it's enabled automatically when using `withSettings().serializable()`.

It still require to have Mockito on the classpath of the JVM classloader where it is deserialized.