Webpack 3 and many fixes

• Fix test runner windows
• Updated to webpack 3
• Use .dockerignore to increase speed of building Docker image (no need to copy files to Docker build context).
• Use npm@6 and add package-lock.json.
• Update versions of nodejs used for testing in Travis (only LTS / actively maintained versions - no more node@4!!).
• Use a single Dockerfile w/ build targets, to greatly speed up building of Docker image.
• Swap default Docker environment from production to development, to improve DX.
• Eliminate production-mode inclusion of devDependencies, to keep production Docker image as light as possible and lower production-mode memory usage.
• Explicitly volume-map all files into Docker container when in dev-mode.
• Removed the --harmony-proxies flag from npm test, as it is no longer supported by nodejs.
• Eliminate different markup warning between client/server during dev