Proper dockerization (separate containers)

[niieani]

I've started working on a proper dockerization of iRedMail. There's still a bit to do, but it looks promising. Basically, I'm hooking the installer so it can run in the build process, switching on or off specific parts of the build. On top of that I'm caching the mysql queries executed during the installation so they can be applied once an instance is up. It was quite a bit of work to get here, but now what's left is putting it all together - those small things like making sure the services talk to each other and not localhost, plus making a wrapper scripts that will boot up the necessary process.

https://github.com/niieani/iredmail-docker

If anybody wants to help out, I'm all for it.