[python] Improve style, add some, use wrapper helpers

python/dumux/__init__.py

+"""The DuMux Python-bindings for using DuMux entirely from Python
+
+DuMux is
+* short for Dune for Multi-{Phase, Component, Scale, Physics, …} flow and transport in porous media
+* a free and open-source simulator for flow and transport processes in porous media
+* a research code written in C++
+* based on Dune (Distributed and Unified Numerics Environment)
+* a Dune user module in the Dune environment
+
+https://dumux.org/
+"""
+
 __import__("pkg_resources").declare_namespace(__name__)