StructuredGridFactory builds YaspGrid without overlap

The specialization Dune::StructuredGridFactory<YaspGrid>::createCubeGrid does not fall back to the default parameters of the YaspGrid constructor. It deliberately sets values for grid periodicity (none) and overlap (0). In my case this caused the obscure situation where I could set up an overlapping parallel solver in PDELab without any errors or warnings, but it computed a wrong solution due to the 'missing' overlap. Everything worked fine when using the YaspGrid constructor with its default values (overlap = 1).

If there's any reason why the GridFactory would overwrite the default overlap setting, please add that to its documentation. If not, I'd like the method createCubeGrid to use the default values of the YaspGrid constructor where possible.