Merge branch 'feature/spatialparams_python' into 'master'

Spatial parameters for Python bindings

Closes #1145

See merge request !3069

(cherry picked from commit 790bdaee)

8e464d6c [dumux][python][spatialparams] update the problem and spatialparams classes
2e25f728 [python][material] remove old spatial params files
56a3c69b [python] Make spatialparams optional and make separate modules in python/common
97d568bb [python] Make spatial params const again