ENH: support multiple zones for topo set sources (#1060)

- uses the keywords 'zones' and 'zone' to avoid potential conflicts
  with a named topoSet action, but accepts 'name' for compatibility.

tutorials/multiphase/reactingMultiphaseEulerFoam/laminar/mixerVessel2D/system/topoSetDict

@@ -24,7 +24,7 @@ actions
         source  zoneToCell;
         sourceInfo
         {
-            name rotor;
+            zone rotor;
         }
     }
 );