vspk-javascript: Support inherited attributes

[killanch]

• updated base_attrs list in config.json
• generated model class will extend NUAuditableEntity if spec extends @audited
• js-bambou PR: https://github.com/nuagenetworks/js-bambou/pull/176

[killanch]

@natabal can you pls review? will not be merged until other lang vspk issues are resolved