Minify image, add seed override

[aimmac23]

Hi,

I deployed this project to my local Kubernetes cluster. I made a few changes:

• Reduce image size from 1.19GB to 166MB by changing base image.
• Add random seed override by environment variable
• Change default HTTP port to 8080 - the previous default will always need changing for Linux development, and makes deploying harder
• Add super-minimal Docker image based on Alpine + PyInstaller (~50Mb). I didn't make it the default because it makes the builds more fiddly.

Thanks :)