small change in constSolidThermo and singleLayerReion

For rotational:
- 180 degree transformation now correct
- use furthest away face to determine rotation
- do not use calculated faceNormals at all

First interpolates from the cells to the vertices and then from the face
vertices to the face centres.  This may be a useful scheme for calculating
gradients on bad/tet meshes when used in conjunction with the Gauss gradient
scheme.

- alternative to WM_PROJECT_INST_DIR/site for systems with locked down
  installation paths (eg, when packaged as RPM or deb)

  When "$WM_PROJECT_SITE" is defined, it is used in favour of
  "$WM_PROJECT_INST_DIR/site"

- can be reused for other (vector, tensor, ...) field types