IMP3 overhaul to cleanup the code and improve the project structure.

Main points: to be updated/discussed

• start using tags
• default snakemake version to be used by all developers
• recommended folder structure (snakemake's best practices)
• configuration: config files, launcher scripts
• integration of external tools
• formatting conventions incl.
  • Python code
  • snakemake code/rules
  • other
• code overhaul
  • general formatting
• (dummy test data, unit tests, CI)

See the linked issues for details.