Support basic auth or without security in OpenAPI generator

[stevehu]

We have a basic auth handler here at https://github.com/networknt/light-4j/tree/master/basic but the generator doesn't support it at the moment. Need to update the OpenAPI generator to support basic and even allow to generate code without security definition.

[stevehu]

Relate to #163

[stevehu]

As the configuration for the light-codegen is getting more complicated, it is not wise to add another option to switch between default OAuth 2.0 to Basic. For users are still interested in basic, replace the OAuth 2.0 handler in the handler.yml will do the trick.