Dockerize ncharts

[erikj]

Pull request for review and discussion:

• dockerizes ncharts by
  • adding configuration to utilize official Python image and support required services via Docker Compose
  • moving hard-coded production paths to environment variables, namespaced w/ NCHARTS_ prefix
• switch from Apache + mod_wsgi to Nginx + gunicorn, for lighter and easier to debug environment
• config: docker/
• documentation: docs/DOCKER.md, docker/README.md
• demo: http://datavis-dev.eol.ucar.edu:8000/

Resolves #15

[erikj]

This isn't the most atomic pull request, but some of the big advantages that it provides:

• Moves the Python execution environment out of package management, so we don't have to build and maintain our own Python 3 packages. Staying up to date on security fixes will be much easier.
• Decouples the web server and the execution environment dependencies by removing mod_wsgi.
• Makes spinning up a new environment much easier, faster, consistent and reliable.