fix pip taking forever and add Dockerfile to simplify testing

Currently the building of the pages fails with

    ERROR: Job failed: execution took longer than 1h0m0s seconds

because of many

    INFO: pip is looking at multiple versions of XYZ to determine which version is compatible with other requirements. This could take a while.
    INFO: This is taking longer than usual. You might need to provide the dependency resolver with stricter constraints to reduce runtime. ...

A manual run on my laptop without hard time limits was not finished after 6 hours.

It will now use basic Debian Python packages whereever possible and only install a dozend or so dependecies with pip.
The runtime is now down again to reasonable time, as it can be tested with the added Dockerfile:

    podman build .

.gitlab-ci.yml

@@ -1,8 +1,8 @@
-image: continuumio/miniconda3:latest
+image: debian:latest
 
 before_script:
-- conda install -y pyzmq
-- pip install jupyter-book sphinxcontrib-bibtex
+- apt-get update && apt-get install -y pip python3-sphinx jupyter-notebook python3-anyio python3-greenlet python3-click python3-jupyter-server python3-sqlalchemy python3-latexcodec python3-nbclient python3-nest-asyncio python3-pybtex python3-pybtex-docutils python3-smmap python3-soupsieve python3-toml
+- pip install jupyter-book
 
 pages:
   stage: deploy

Dockerfile

@@ -0,0 +1,11 @@
+FROM debian:latest
+
+RUN apt-get update
+RUN apt-get install -y pip python3-sphinx jupyter-notebook python3-anyio python3-greenlet python3-click python3-jupyter-server python3-sqlalchemy python3-latexcodec python3-nbclient python3-nest-asyncio python3-pybtex python3-pybtex-docutils python3-smmap python3-soupsieve python3-toml 
+RUN pip install jupyter-book
+
+RUN mkdir -p /root/documentation
+COPY * /root/documentation
+RUN cd /root/documentation && jupyter-book build .
+
+# TODO make build book accessible through a webserver