Setup a docker development environment

[calh]

Hi @thiagopradi,

I'll submit another PR later for addressing a bug I found in octopus. For now, I wanted to contribute a docker compose system to make it easier for developers to dive into patches on your project. I was struggling with the mysql and postgres setups without passwords, and Docker seemed like the way to go here.

I've added instructions to the README on how to get started with development. The docker-compose.yml will load up mysql, postgres, and run the test suite when starting up the stack.

Let me know if you have any questions or concerns!

[thiagopradi]

@calh - this looks awesome! I'm on a pretty busy week - but I'll review this PR this weekend.