STYLE: avoid unrestricted dictionary lookup in conversion, sampling, surfMesh

- aids with detection of excess tokens (issue #762)

- deprecated dictionary::operator[] in favour of the lookup() method
  which offers more flexibilty and clarity of purpose.
  Additionally, the read<> and get<> forms should generally be used
  instead anyhow.

src/sampling/sampledSet/patchCloud/patchCloudSet.H

@@ -65,7 +65,7 @@ class patchCloudSet
     // Private data
 
         //- Sampling points
-        const List<point> sampleCoords_;
+        const pointField sampleCoords_;
 
         //- Patches to sample
         const labelHashSet patchSet_;