Lenient deserialization

**Is your feature request related to a problem? Please describe.**
It may be desired to deserialize a CAS JSON document into a CAS that contains only a subset of the types present in the JSON document. Currently, this produces an error.

**Describe the solution you'd like**
A configuration parameter enabling a lenient deserialization mode as we also have it for XMI files which simply skips feature structures of types that are not defined in the target CAS.

Start by locating the CAS JSON deserializer and the existing XMI lenient-deserialization configuration. Trace how undefined types currently cause errors, then define and test a mode that skips unsupported feature structures while preserving the types available in the target CAS.

Written by the indexing model from the issue text.