[python] Add first Python bindings for the TimeLoop and the GridGeometry

CMakeLists.txt

dumux/python/CMakeLists.txt

dumux/python/common/CMakeLists.txt

dumux/python/common/timeloop.hh

dumux/python/discretization/gridgeometry.hh

python/CMakeLists.txt

python/dumux/CMakeLists.txt

python/dumux/common/CMakeLists.txt

python/dumux/common/__init__.py

python/dumux/common/_common.cc

python/dumux/discretization/CMakeLists.txt

python/dumux/discretization/__init__.py

python/setup.py.in