STYLE: separate areaNormal/unitNormal method for primitives (issue #885)

src/OpenFOAM/meshes/meshShapes/face/face.C

src/OpenFOAM/meshes/meshShapes/face/face.H

src/OpenFOAM/meshes/meshShapes/face/faceContactSphere.C

src/OpenFOAM/meshes/meshShapes/face/faceI.H

src/OpenFOAM/meshes/meshShapes/triFace/triFace.H

src/OpenFOAM/meshes/meshShapes/triFace/triFaceI.H

src/OpenFOAM/meshes/primitiveShapes/cut/cut.H

src/OpenFOAM/meshes/primitiveShapes/cut/cutTemplates.C

src/OpenFOAM/meshes/primitiveShapes/plane/plane.H

src/OpenFOAM/meshes/primitiveShapes/pyramid/pyramidI.H

...OpenFOAM/meshes/primitiveShapes/tetrahedron/tetrahedron.H

...penFOAM/meshes/primitiveShapes/tetrahedron/tetrahedronI.H

src/OpenFOAM/meshes/primitiveShapes/triangle/triangle.H

src/OpenFOAM/meshes/primitiveShapes/triangle/triangleI.H

src/lagrangian/basic/particle/particle.H

src/lagrangian/basic/particle/particleI.H