Set up Babel to compile API TypeScript code

[iquabius]

Blocked: Babel doesn't support namespaces, and 'graphql-code-generator' uses them. See babel/babel#8244.

TypeScript With Babel: A Beautiful Marriage

• It doesn't seem that beautiful, see Replace TSLint with ESLint #51.

TypeScript and Babel 7 (MS Blog)

Microsoft/TypeScript-Babel-Starter

{
  "scripts": {
    "build:babel": "rimraf dist-babel && npm run ws:babel -- ./src --out-dir dist-babel --extensions '.ts,.tsx'",
    "ws:babel": "../node_modules/@babel/cli/bin/babel.js"
  }
}