Here, we make it possible to add a "-nightly" suffix to the package
version. This suffix will find its way to the Docker image tags. Thus,
the nightly branch will have different image tags. This will resolve
some confusion, as image tags are currently identical in nightly and
master.
In Maple, the plugin API is slightly different: the apk file is built and
stored in the android-app Docker image, then served by a simple Caddy file
server. This makes it easy to distribute the apk to students.
