ENH: primitiveMesh: make geometry calculation runtime selectable

This adds a 'geometry' scheme section to the system/fvSchemes:

geometry
{
    type            highAspectRatio;
}

These 'fvGeometryMethod's are used to calculate
- deltaCoeffs
- nonOrthoCoeffs
etc and can even modify the basic face/cellCentres calculation.

applications/utilities/mesh/manipulation/splitMeshRegions/splitMeshRegions.C

@@ -680,7 +680,7 @@ autoPtr<mapPolyMesh> createRegionMesh
             regionName,
             mesh.time().timeName(),
             mesh.time(),
-            IOobject::NO_READ,
+            IOobject::READ_IF_PRESENT,  // read fv* if present
             IOobject::AUTO_WRITE
         ),
         mesh