Resolve "replace pipenv with poetry"

Closes #55 (closed)

tasks to do:

• create pypi.org account (@hueser93)
• create version tag v0.1.0 to mark version used for survey 2019/2020 (@hueser93)
• determine proper license (@mdolling-gfz) (mby add sqa if i find the time to add poetry there)
• replace pipenv with poetry (@mdolling-gfz , assisted by @schlauch)
  • the actual requirements are in the setup.py
• update CI to use poetry (@mdolling-gfz)
• update docs for installation and usage (@mdolling-gfz)