Refactored dockerfile and development process

[Matra-Master]

I wanted to make more than one keyboard config at the same time and found several optimizations that could be done to the docker structure in order to facilitate that development case. I think I made every commit extensive in it's descriptions but this is a tldr:

• Removed a lot of unnecesary steps from the dockerfile
• Removed three files in main that are configs for specific keyboards
• Modified the dockerfile so it picks files from one of the keyboards and adds them to the container during docker build
• Added an env variable to the Dockerfile so the keyboard files are kind of interchangeable during a docker build

My motto approaching this was "If I have to modify the README to explain something then I'm doing this wrongly"

[Matra-Master]

I forgot about building outside of containers! That's a good point. I should rewrite the Dockerfile a little more then. Thanks!