WIP: Feature/example rot sym
Fixes #787 (closed)
ToDos:
- Update documentation, especially in spatialparams
- explain rotationsymmetricgridgeometrytraits
- write 1p equation in radial coordinates and specify analytical solution
- generate and include result pictures
- maybe also explain how the paraview filter can be used for visualization
- Move calculate L2 error to main.cc
- Move add vtk output to main.cc