Generalize input option for deactivated region to be a rectangular prism

[stvdwtt]

Currently we have an input option in the geometry block of the input file to deactivate elements above a certain height (material_height). For certain simulations, especially of "repair" processes, we may want to deactivate a smaller subset of the mesh. A straightforward generalization of the current capability would be to specify corners of an axis-aligned rectangular prismatic domain to deactivate.

For complex geometries, we'd probably want to mark this in the input mesh in some way, but this would provide a lightweight capability that could be used in some cases.