ENH: mergeOrSplitBaffles - remove boundaries with zero faces after merging

Add an option (or do automatically) in mergeOrSplitBaffles to remove boundaries with zero faces from the boundary file after merging. Prevents the need to run createPatch after merging.

Also, as an aside, mergeOrSplitBaffles.C says in its header that there is a -merge command line option, but it does not exist. However, there is a -split option. Can this be made consistent?

## Reattaching the author to the issue ticket: @graups ##