Draft: Bug in BoxDfm model
Don't merge. This is just for discussion.
When working on the new local dof concept !3946 (merged) I think I found a bug in the BoxDfm model. It seems that in this model local residual contributions are added up twice.
This is a temporary MR to show the bug. I have modified the boxdfm test case such that it allows to disable the fracture contributions in the local residuals. Then, one would assume that it exactly matches the solution of the classical Box2pModel.