Adds validateObject and registers it in standardValidators for object types
Registers validateDate in standardValidators for datetime types (it's already registered for date types)
Introduces the concept of an unknown validator to allow for a catch-all for validating types that don't have a registered validator (similar to the unknown serializer concept). This can be used as a no-op, or to log an error, or even to throw an exception.
Performs the tasks discussed in #857:
validateObjectand registers it instandardValidatorsforobjecttypesvalidateDateinstandardValidatorsfordatetimetypes (it's already registered fordatetypes)unknownvalidator to allow for a catch-all for validating types that don't have a registered validator (similar to theunknownserializer concept). This can be used as a no-op, or to log an error, or even to throw an exception.Closes #857