Add gapMode and gapLevels setting in refirment section

[mactone]

Current refinement have "Volume Refinement Level".
Is it possible to add gapMode and gapLevels setting under the volume refinement, so the small gap in the geometry can be meshed without too much volume refinement.

[tkeskita]

Thanks, I'll put this on my TODO list, although not sure when I will have time to add this.