improvements foamToEnsightParts

Currently foamToEnsight and foamToEnsightParts perform somewhat differently.

• foamToEnsight works in serial/parallel, but does not handle cellZones
• foamToEnsightParts handles cellZone, but only works in serial

Desirable to retain cellZone information in parallel as well, which implies making foamToEnsightParts parallel-aware. Explore the possibility of merging some foamToEnsightParts aspects into ensightMesh (ie, foamToEnsight) and enabling/disabling on a switch.

Cross-ref: EP1109