Added support for allOf and oneOf

[gcutulenco]

• added interface to extend logic responsible for getting key (schema id) for a type
• added interface to find discriminator information
• was not sure what was the purpose of internal settings, switched implementation to use schema generation settings class
  • unit tests forced this class and all its properties to be serializable
• added logic to registry to include child-parent class information as allOf, oneOf

[ghost]

All CLA requirements met.