Containerized version of FSL FIX
This is based very closely on the excellent tutorial by NeuroSnippets (https://neurosnippets.com/posts/fslfix-in-a-box/#post). I've reordered the build to make rebuilding it faster if you mess with things other than the dependencies, added some informative tags, and fixed how NeuroDebian packages are accessed (for some reason the build died when I tried it as specified in the article).
I've also added some support scripts for building and testing, and converting to singularity containers (what we use on our cluster).