Re-add transit demo

[tnation14]

Re-adds the transit demo to the carousel, which was removed in #68.

Changes:

• Revert HTML/JavaScript changes made in #68
• Updated static/js/demo/transit.js to make WMS requests to https://transit.geotrellis.io/api/travelshed/wms2, which can handle uppercase query string parameters.
• Added volumes to docker-compose.yml so that gtsite-nginx picks up updates to static files without rebuilding the container.
• Prefix CloudFront logs with CloudFront/Site to differentiate from other CloudFront distributions using the same logs bucket.

Testing

• Build static assets, and start nginx

  $ make clean
  $ docker-compose build gtsite-assets
  $ docker-compose run --rm gtsite-assets
  $ ./scripts/server

• The site will be available at http://localhost:8080. Ensure that the transit demo is in the carousel.