support allOf and anyOf in schema definitions

[satra]

when an object in a json schema has anyOf, the current function JsonSchemaImportEngine().translate_schema does not seem to traverse the types in anyOf and generates the following error.

ERROR:root:Cannot translate type None in {'anyOf': [{'type': 'string'}, {'type': 'null'}], 'default': None, 'title': 'Model'}