warnings about missing python pop up every now and then.

docker hub bug. Attempt to work around it.

Revert "Docker hub's build context has changed, leading to build errors. Luckily this new method is more convenient for us anyway since we"

This reverts commit 68907330.

Docker hub's build context has changed, leading to build errors. Luckily this new method is more convenient for us anyway since we
can get rid of the useless duplicate copies.

Concentrate everything on the master branch. It's way, way easier to manage the different images this way.