ENH: Initial commit of new runTimePostProcessing function object

- Allows generation of images (currently PNG files) during the run
- ... or afterwards by invoking the execFlowFunctionObjects utility
- Wrapper around VTK functionality
- Support for objects:
  - text
  - points (glyphs: sphere, arrow)
  - lines (tubes)
  - surfaces (wireframe, shaded, combination)
- Colour using:
  - user-defined
  - field values (several colour maps availale)
- For image sequences:
  - dynamic views (camera movement)
  - objects can appear/disappear using opacity
- Building
  - VTK dependency v6+
  - satisfied using ParaView from ThirdParty directory
  - or separate VTK installation