Fix python codestyle

Matplotlib test refactoring (Follow-on PR #1169)

Activate conda base environment by default

Stack update

Add `cm-super` package install to `scipy-notebook` required for `matplotlib` latex labels.

Some conda packages rely in the `conda activate` to set the corresponding environment variables, therefore just including the `bin` directory in the `PATH` is not sufficient.

Update Dockerfile fix spelling

- miniconda versions and arguments
- remove useless hd5 install (dependency of h5py)
- pin the version of pyarrow

Following images updated

- `base-notebook`
- `scipy-notebook`
- `tensorflow-notebook`
- `tensorflow`
- `datascience-notebook`
- `r-notebook`

Spark 3.0.1 -> fixes #1156

Added a note in the documentation to indicate that the build will only work with Spark current versions.

Added a note in the documentation to indicate that the build will only work with Spark current versions.

Changed `""` into `''` to pass an empty token. Seems to be linked to this warning:
```
/opt/conda/lib/python3.8/site-packages/traitlets/traitlets.py:2195: FutureWarning: Supporting extra quotes around Unicode is deprecated in traitlets 5.0. Use '' instead of "''" – or use CUnicode.
```

Added debug information (ouput of the command line).

Add -f option with groupadd to gracefully exit when adding existing groups

Signed-off-by: Greg <werner.greg@gmail.com>

base-notebook: Update notebook to 6.1.3 and jupyterlab to 2.2.5

update to julia 1.5.0

Resolves #1131: Allow alternative Spark version

Resolve Docker lint (hadolint) errors