nbconvert + inkscape test improvements

recipes: use COPY with --chown for jovyan's files

Update docker stacks 2020-11-20

The following changes have been made.

- `base-notebook`
  - `Changed`: Bump Ubuntu
  - `Changed`: Bump conda
  - `Fixed`: Add missing `apt-get clean`
- `minimal-notebook`
  - `Removed`: `jed` editor see #1174 (partial)
  - `Deprecated`: `emacs` editor (in the documentation and in the image) see #1174 (partial)
- `scipy-notebook`
  - `Fixed`: Add missing `apt-get clean`
  - `Changed`: Bump `dask`
  - `Changed`: Bump `protobuf`
- `r-notebook`
  - `Changed`: Bump `r-base`
  - `Changed`: Bump `r-rmarkdown`
  - `Removed`: The description of `tidyverse` packages because it's not the place to do that and it will always be obsolete.
- `datascience-notebook`
  - `Changed`: Bump `r-base` to `4.0.x` see #1102 (partial)
  - `Removed`: `plyr` package because it's retired fixes #1103
  - `Removed`: `r-reshape2` package because it's retired fixes #1103
  - `Changed`: Bump `r-rmarkdown`
  - `Changed`: Bump Julia
- `tensorflow-notebook`
  - `Changed`: Bump `tensorflow`
- `pyspark-notebook`
  - `Fixed`: Add missing `apt-get clean`
  - `Changed`: Bump `pyarrow`
- `all-spark-notebook`
  - `Fixed`: Add missing `apt-get clean`
  - `Changed`: Bump `r-base` to `4.0.x` see #1102 (partial)
  - `Changed`: Bump `r-sparklyr`

Run pre-commit hooks server side

By default, Dockerfile's COPY creates files and directories with UID and
GID 0. (See https://docs.docker.com/engine/reference/builder/#copy)
When we put them in jovyan's $HOME or want jovyan to manipulate these
files, they should be owned by jovyan instead.

Specifically
https://jupyter-docker-stacks.readthedocs.io/en/latest/using/recipes.html#add-a-python-3-x-environment
failed with a "permission denied" error when the code for using an
environment.yml file was uncommented. I assume some of the other recipes
might have failed like that, too, but I didn't test them.

nano -> nano-tiny

Fix bashate style issues

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