The auto wrapping functionality for MPISolverWrapper looks correct and straightforward to me. A check for function type is already included in the HyppopySolver.

The cleanup of the mpiplayground makes sense for now. We need to convert it to a "proper example" and move into the right folder. Additionally the possibility to pass a custom comm should be explained. I spawned T28349 for this. This has no effect on this commit. Here everything looks fine.