Add InheritanceMode setting

[RicoSuter]

The problem is that for validation we need oneOf inheritance (ie define the child classes): #13

... and for swagger generation we need allOf inheritance (ie define parent classes)

Idea:
In the C# type to schema generator we should have an option to choose the InheritanceMode:

• AllOf (default): OpenAPI style allof inheritance (ie base types are defined with allof)
• OneOf: JSON Schema style oneof inheritance (ie subtypes are defined with oneof)

[RicoSuter]

Also support code generators...