Added numbering on searhableSurfaceCollection.

- moved to $FOAM_LIBBIN/paraview so that built libraries sit in their
  own folder - avoids PV error msgs on start-up when it tries to load
  all libs under the $PV_PLUGIN_PATH

- using chemical enthalpy instead of total enthalpy

- Re-setting initial T fields to unitialised values prior to running
  setFields utility

- Retrieve h directly from thermo package instead of using look-up

- removed repeated declaration of pure abstract functions
- added function to return the turbulence effective thermal diffusivity
  for a patch

- Corrected calculation of temperature gradient
- Option to specify the heat source in terms of a power [W] or flux [W/m2]

- Updates to enable correct operation in parallel
- Added weighted average operation for cell sources