Interpreter: Binary de-serialization: Move Schema and normalizer reloading to ContextIndex get functions

[chrisreu]

When ContextSchema gets deserialized, there is some state-dependend data missing: The ContextType implementation and the normalizer implemetation.

Right now the Interpreter is responsible to reload those implementations after deserializing. This should happen in the Get functions of ContextSchema, just like we do it for IndexImpl.