Needs to be consolidated with multiphaseInterFoam with thermal and
compressibility effects made run-time selectable

fixedFluxPressure BC: the snGrad is now pushed into the BC from pEqn.H rather than being evaluated in the BC

Multiphase: Update all solvers to accommodate the split between twoPhaseMixture and incompressibleTwoPhaseMixture

This reverts commit c5bea524.

This reverts commit b18f6cc1.

Exception: applyWallFunctionBoundaryConditions.C cannot split #include
directives.

uniformDimensionedVectorField.

location for the specification is the same as that for the pd level.

- change system/controlDict to use functions {..} instead of functions (..);
  * This is internally more efficient
- fixed formatting of system/controlDict functions entry

- pedantic change: use 'return 0' instead of 'return(0)' in the applications,
  since return is a C/C++ keyword, not a function.

Changed formatting of interDyMFoam