Changed handling of impact defaults in SemiExplicitEulerTimeStepper. The default now is that the capture, minCOR, and friction transition velocities all default to twice the constraint tolerance. This way by default you get exactly the COR you asked for, rather than the fancier velocity-scaled one. That should only be used if requested because, for example, it is confusing to see a non-zero COR when you set the COR to zero.