Readability cleanup & minor fixes

[AsavarTzeth]

I redid all my improvements and split it all up into 4 commits.

First I added a badly needed .dockerignore file. It will save you a lot of time when we don't add the entire git history to the build containers.

Secondly I did a cleanup of the main Dockerfile, including the changes that somehow made my issues disappear.

Thirdly I fixed your Debian base Dockerfile, that did not follow some best practices regarding the apt cache & layering. Simply put, if Debian pushes updates to the package repositories at the wrong time (no matter how unlikely) things could break.

Lastly I changed all white spaces into tabs, added empty new line separators and minor readability tweaks.on most scripts and all the rest of the Dockerfiles.

If you prefer 2 spaces long indentation, I recommend using an editor that supports setting a custom length (which only works if you use tabs). Thus to make things easier for potential contributors I recommend tabs.

As you might see in the comments of the bootstrap.sh file, I did figure out the role of the loop and the if statement.

But I could never figure out why it needed to be run 3 times, instead of just 2. Changing it to a 2 times loop resulted in images of exact same size and contents. I also discovered a minor time saver that could be easily implemented if the muslbase-runtime and muslbase-static-runtime only was created the last loop run.

All of that I will address in a second pull request, after we have had time to discuss this one. I figured that was a slightly larger issue and a slightly greater chance of me missing something.