ENH: provide low-level bound box() methods for meshShapes

- box method on meshShapes (cell,edge,face,triangle,...)
  returns a Pair<point>.

  Can be used directly without dependency on boundBox,
  but the limits can also passed through to boundBox.

- Direct box calculation for cell, which walks the cell-faces and
  mesh-faces.  Direct calculation for face (#2609)

applications/test/primitivePatch/Test-PrimitivePatch.C

@@ -232,6 +232,7 @@ int main(int argc, char *argv[])
         const labelListList& edgeFaces = pp.edgeFaces();
         const labelListList& faceEdges = pp.faceEdges();
 
+        Pout<< "box: " << pp.box() << endl;
 
         checkFaceEdges(localFaces, edges, faceEdges);