ENSDC: Accept namespace datacontract attribute for enums

[anttipih-predisys]

The GetNamespace method for CodeClass items used the GetDataContractName method to check for a DataContract(Namespace) attribute before defaulting to the GetNamespace method. An overload implements GetDataContractName so that GetNamespace can check for data namespace contracts for CodeEnum items as well.

[madskristensen]

Thanks