[WIP] Communicate over intersections
Make it possible to communicate over intersections in yasp grids. This works similar to communication for codim 1 entities but builds the corresponding Dune intersection beforehand. This makes it possible to get the corresponding codim 0 entity that lives on the same processor in the gather and scatter method of the DataHandle.
A possible use case are nonoverlapping Discontinuous Galerkin methods. By using intersection communication we can avoid overlapping grids, additional degrees of freedom and their constraints. We have an implementation for this in pdelab (for convectiondiffusiondg) that needs some cleanup before sharing ;).
Note: Right now the function communicateIntersection in yaspgrid.hh is mostly code duplication of communicateCodim. This will of course get fixed. The purpose of this merge request is to have a place for discussion of the intersection communication feature. If you have any comments on implementation or interfaces feel free to leave it here.