BUG: polyMesh removeFiles side-effect for blockMesh viewer (issue #346)

- polyMesh constructor from cell shapes invoked 'removeFiles'.
  This may or may not be what the caller wants or expects.
  With the ParaView blockMesh viewer, this behaviour causes deletion of
  all mesh data (points, faces, etc) when the viewer is refreshed.

  Triggered even when just building the blockMesh topology.

- only a few places that construct a polyMesh from cell shapes
  (mostly mesh conversion utilities).
  Ensure that the file removal (if any) occurs in the application
  and *not* as a side-effect of calling the polyMesh constructor.

--

  blockMesh (application)
    - The placement of the removeFiles seems to also remove freshly
      generated sets (Bug or feature to remove sets?)

  +-----------------------+---------------+------------------+
  | Application           | Constructor   | removeFiles      |
  |                       | (patch info)  | new / existing   |
  +-----------------------+---------------+------...