Snakemake

- Various textual improvements in the tutorial (dlaehnemann).

- No longer use a shortened hash for naming conda environments in
.snakemake/conda (johanneskoester).
- Various little updates to the docs (johanneskoester).

- Fix race condition in conda checking code (johanneskoester).

- Restored Python 3.5 compatibility by removing f-strings (mbhall88)
- Fix rendering issue in the docs.
- Add gitpod dev environment and gitpod environment for the tutorial.

- Introduced a new module system, see
<https://snakemake.readthedocs.io/en/stable/snakefiles/modularization.html#modules>
(johanneskoester).
- Introduced a rule inheritance mechanism, see
<https://snakemake.readthedocs.io/en/stable/snakefiles/rules.html#rule-inheritance>
(johanneskoester).
- Automatically containerize a conda-based pipeline with
`--containerize`, see
<https://snakemake.readthedocs.io/en/stable/snakefiles/deployment.html#containerization-of-conda-based-workflows>
(johanneskoester).
- Use temporary files for long shell commands (epruesse).
- Various fixes in the documentation (ctb, SilasK, EthanHolleman).
- Fixed a bug in job grouping that led to non-deterministic behavior
(johanneskoester).

Changed

- Fixed infinite loading of results in Snakemake
reports (FelixMoelder)