surfaceFeatures: Added optional input of maximum angle between opposite points considered close

To handle the additional optional specification for the closeness calculation
these settings are now is a sub-dictionary of surfaceFeaturesDict, e.g.

    closeness
    {
        // Output the closeness of surface elements to other surface elements.
        faceCloseness           no;

        // Output the closeness of surface points to other surface elements.
        pointCloseness          yes;

        // Optional maximum angle between opposite points considered close
        internalAngleTolerance  80;
        externalAngleTolerance  80;
    }

tutorials/mesh/snappyHexMesh/pipe/system/surfaceFeaturesDict

@@ -47,8 +47,11 @@ pipeWall
     // - 180: selects all edges
     includedAngle           150;
 
-    // Output the closeness of surface points to other surface elements.
-    pointCloseness          yes;
+    closeness
+    {
+        // Output the closeness of surface points to other surface elements.
+        pointCloseness          yes;
+    }
 
     writeVTK                yes;
 }