Add Method to Legacy Ghost Cells Generator to match Ghost Cells Generator for setting ghost level
The legacy ghost cells generator needs to have the same method for setting ghost levels so that if the two are swapped, the methods don't also have to be swapped. So LegacyGCG::MinimumNumberOfGhosts(int) should wrap LegacyGCG::.MinimumNumberOfGhostLevels(int) This will alleviate a ton of headache for users needing to swap between the two GCGs.