Schwarz Contact: implement non-smooth contact

[ikalash]

We need to enable the case of non-smooth contact, for example, a sharp feature like a kink or corner coming into contact against a smooth surface. This case is pervasive when you have fragmentation or impact. We need to figure out how to apply Schwarz BCs in this case. In particular, if you have an impact at a single point, one needs to take that single node information and transform it into a traction.