produce docker build speedup
- git checkout produce docker cache invalidation, do it when needed
- use /opt/app PATH for the two containers
- use two different layers: one to do the pip requirements, the other
for the rest of the sourcecode
this repo is a reinitialization with a change in the concept
previous repo had git subtree of django-musician and django-orchestra,
that was too static for our interest
next approach is a script that pulls git repos, and that would be
needed if you want to build everything, if not, just with the docker
compose you would have enough for running the containers, hence,
downloading the images from the docker registry
