Reclaim some of the size lost by splitting the cell catalogs

[ISSOtm]

There is already somewhat considerable padding within a cell catalog, and splitting the catalog in two in a913a51 has multiplied the padding by 2.5!

This can be mitigated by fusing the two catalogs like they were before a913a51 when possible; then both labels are identical, and only a single header byte is wasted. However, that increases teNOR's complexity significantly.