ENH: Added run-time selectable sources to compressible solvers

applications/solvers/compressible/rhoPimpleFoam/EEqn.H

applications/solvers/compressible/rhoPimpleFoam/Make/options

applications/solvers/compressible/rhoPimpleFoam/UEqn.H

...cations/solvers/compressible/rhoPimpleFoam/createFields.H

applications/solvers/compressible/rhoPimpleFoam/pEqn.H

...ations/solvers/compressible/rhoPimpleFoam/rhoPimpleFoam.C

...rs/compressible/rhoPimpleFoam/rhoPimplecFoam/Make/options

.../solvers/compressible/rhoPimpleFoam/rhoPimplecFoam/pEqn.H

...ompressible/rhoPimpleFoam/rhoPimplecFoam/rhoPimplecFoam.C

...ible/rhoPimpleFoam/rhoPorousMRFLTSPimpleFoam/Make/options

...oam/rhoPorousMRFLTSPimpleFoam/rhoPorousMRFLTSPimpleFoam.C

...essible/rhoPimpleFoam/rhoPorousMRFPimpleFoam/Make/options

.../compressible/rhoPimpleFoam/rhoPorousMRFPimpleFoam/UEqn.H

.../compressible/rhoPimpleFoam/rhoPorousMRFPimpleFoam/pEqn.H

...impleFoam/rhoPorousMRFPimpleFoam/rhoPorousMRFPimpleFoam.C

applications/solvers/compressible/rhoSimpleFoam/EEqn.H

applications/solvers/compressible/rhoSimpleFoam/Make/options

...cations/solvers/compressible/rhoSimpleFoam/createFields.H

applications/solvers/compressible/rhoSimpleFoam/pEqn.H

.../compressible/rhoSimpleFoam/rhoPorousMRFSimpleFoam/EEqn.H