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

Rewrote tests. There's now a routing test that checks all the endpoints and methods in the openapi.yaml, and checks that a proper request (using samples automatically created for schema) returns a valid 200. Not all tests pass - there's no support for application/xml, and work needs to be done on dataForms. Added mode classes, but they are not part of the system flow yet.