ENH: snappyHexMesh: add automatic gap-level detection and refinement

...s/utilities/mesh/generation/snappyHexMesh/snappyHexMesh.C

...utilities/mesh/generation/snappyHexMesh/snappyHexMeshDict

src/OpenFOAM/algorithms/indexedOctree/volumeType.H

src/mesh/autoMesh/Make/files

...autoMesh/autoHexMesh/autoHexMeshDriver/autoRefineDriver.C

...autoMesh/autoHexMesh/autoHexMeshDriver/autoRefineDriver.H

...mesh/autoMesh/autoHexMesh/meshRefinement/meshRefinement.C

...mesh/autoMesh/autoHexMesh/meshRefinement/meshRefinement.H

...toMesh/autoHexMesh/meshRefinement/meshRefinementBaffles.C

...Mesh/autoHexMesh/meshRefinement/meshRefinementGapRefine.C

...utoMesh/autoHexMesh/meshRefinement/meshRefinementRefine.C

...oMesh/autoHexMesh/refinementSurfaces/refinementSurfaces.C

...oMesh/autoHexMesh/refinementSurfaces/refinementSurfaces.H

src/mesh/autoMesh/autoHexMesh/shellSurfaces/shellSurfaces.C

src/mesh/autoMesh/autoHexMesh/shellSurfaces/shellSurfaces.H

src/meshTools/Make/files

...ompositionMethods/hierarchGeomDecomp/hierarchGeomDecomp.C