decode_json / encode_json functions should work with oneOf / anyOf schema options

[nadavMiz]

Environment info

• NooBaa Version: master

Actual behavior

1. currently encode_json decode_json functions in postgres_client.js don't deal with oneOf / anyOf case of schemas. this may lead to objects using those schemas not being properly stored/retrieved from the Postgres database

Expected behavior

1. encode_json/decode_json should parse schemas with oneOf/anyOf cases.

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