ENH: Added new createViewFactors utility

Creates view factors for the view factor radiation model. Planned to replace/deprecate the viewFactorsGen application in a future release.

Cross-ref EP#1418

User-selectable models:

• raySearchEngine: model to generate rays, i.e. face-to-face connections
• viewFactorModel: model to compute the view factors
  • note: hard-coded to use the Hottel model in 2D

For visualisation, use:

• Write the view factors as a volume field

  writeViewFactors    yes;

• Write the rays using OBJ format:

  writeRays       yes; // default = no

Participating patches must be in the viewFactorWall group, i.e. using the inGroups entry of the <case>/polyMesh/boundary file.

myPatch
{
    type            wall;
    inGroups        2(wall viewFactorWall);
    ...
}

Reads:

• <constant>/viewFactorsDict : main controls
• <constant>/finalAgglom : agglomeration addressing (from faceAgglomerate)

Generates:

• <constant>/F : view factors (matrix)
• <constant>/mapDist : map used for parallel running
• <constant>/globalFaceFaces : face addressing

@Prashant - can you run the brake model?

Couple of small cases initially put together as part of the GPU pilot project by Polimi:

annulus2D.tgz cavity.tgz