Improve nodejs lambda with modern javascript && add v2 payload support

[mboisnard]

Issue #, if available:
N/A

Description of changes:

• Improved Nodejs lambda using builder pattern and modern javascript (inspired by Update nodejs example to ES7 and Node v8.10 runtime #24 gist code)
• Added support of API Gateway v2 payload (create authPolicy from event.methodArn or event.routeArn depending on payload) (inspired by Added payload format version 2 blueprints for Node.js and Python #35)
• Changed object based authPolicy to function based authPolicy
• Added public methods documentation only (avoid overdocumentation of internal methods)
• Added examples of using authPolicy Builder methods

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[mboisnard]

@fwenjing12 what do you think about this?

I've also fixed the conflict with "restapiid/region/stage placeholder" commit.