ENH: snappyHexMesh: initial version of directional refinement

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

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

src/mesh/snappyHexMesh/meshRefinement/meshRefinement.C

src/mesh/snappyHexMesh/meshRefinement/meshRefinement.H

src/mesh/snappyHexMesh/meshRefinement/meshRefinementRefine.C

src/mesh/snappyHexMesh/shellSurfaces/shellSurfaces.C

src/mesh/snappyHexMesh/shellSurfaces/shellSurfaces.H

...sh/snappyHexMesh/snappyHexMeshDriver/snappyRefineDriver.C

...sh/snappyHexMesh/snappyHexMeshDriver/snappyRefineDriver.H