Nodejs express server

Created by: YishTish

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh, ./bin/openapi3/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\. If contributing template-only or documentation-only changes which will change sample output, be sure to build the project first.
• Filed the PR against the correct branch: master, 4.1.x, 5.0.x. Default: master.
• Copied the technical committee to review the pull request if your PR is targeting a particular programming language.

Description of the PR

New PR, replacing the previous one that was created last week, and failed build. After understanding the flow better from @wing328, I've synced my end prior to creating the PR. Hopefully tests will be smoother this time. Added new controllers, which should be generated automatically based on openapi.yaml. Notice that index.js has inclusions to all controller files. codegen should relate to that as well. Controller.js is a behavior general class, with static methods that apply to all controllers. Routingtests.js runs through all the operations described in the openapi.yaml and confirms that a 200 is returned. Not all tests work, as there's no support for XML, and formData is still work-in-progress.