LCM: In new STK, get_cell_topology for stk::mesh::MetaData no longer returns
a reference, unlike most other accessors that actually do. This unnoticed
(by me) change led to subtle bugs. The Topology class now deals with copies
of cell topologies instead of references. shards::CellTopology is now
essentially a container for a pointer that points to the actual data.

VTK output boundary function reworked for shortness and efficiency.
Clean up warning in CMakeLists.txt.