mypy usage improvements #93

• Datenguide Python version: 0.2.2

Description

In order to improve code quality and qa the mypy configuration could be improved, which includes. This would be particularly helpful with respect to external dependencies, such that imports don't default to the Any type.

Particular steps would be

• check/improve the mypy configuration files
• introduce mypy stub files, i.e. .pyi files containing stubs for depdncies. These could either be from a repository if available or these could be written explicitly (for the subset of required functions).
• systematically check the code for the presence of type annotations (especially for the return values) and fill in missing annotations. This is particularly important if functions don't have any annotations at all, as these are ignored by mypy