Reformulate plate with hole with Neumann BCs

[srosenbu]

Currently the plate with hole uses only Dirichlet BCs. For the Tool-independent description of the problem it would be nice to have both Dirichlet and Neumann BCs in the Problem.

[joergfunger]

The URI to reference our problem that should also be added to the wiki is https://portal.mardi4nfdi.de/wiki/Model:6775296