improve usability

[bprodoehl]

This container was a great start, but I ran into a few roadblocks that I ended up addressing in what is sort of a fork, here: https://github.com/bprodoehl/docker-scumblr

Enough is different that I started it as a new repo, but I'd love to get some feedback.

Major changes:

• Move to Phusion Passenger as the base container
• Embed Sketchy
• Add environment variables for user, password, and database configuration
• Make it easy to use a linked MySQL container (and address the UTF8 charset issue)

I get Sketchy without Scumblr, but I don't really get Scumblr without Sketchy, so keeping them separate didn't seem worth the extra configuration steps for the user to me. Anyways, if any of this seems worthwhile, I can pull some of these changes to a proper fork and start issuing pull requests.