Descriptions of solvers corrected and made more consistent and more user-friendly

applications/solvers/DNS/dnsFoam/dnsFoam.C

applications/solvers/basic/potentialFoam/potentialFoam.C

applications/solvers/combustion/chemFoam/chemFoam.C

applications/solvers/combustion/fireFoam/fireFoam.C

...ctingFoam/rhoReactingBuoyantFoam/rhoReactingBuoyantFoam.C

...ible/rhoCentralFoam/rhoCentralDyMFoam/rhoCentralDyMFoam.C

...ions/solvers/compressible/rhoCentralFoam/rhoCentralFoam.C

...essible/rhoPimpleFoam/rhoPimpleDyMFoam/rhoPimpleDyMFoam.C

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

...e/rhoSimpleFoam/rhoPorousSimpleFoam/rhoPorousSimpleFoam.C

...ations/solvers/compressible/rhoSimpleFoam/rhoSimpleFoam.C

...olvers/compressible/sonicFoam/sonicDyMFoam/sonicDyMFoam.C

applications/solvers/compressible/sonicFoam/sonicFoam.C

...ications/solvers/discreteMethods/dsmc/dsmcFoam/dsmcFoam.C

...lecularDynamics/mdEquilibrationFoam/mdEquilibrationFoam.C

...solvers/discreteMethods/molecularDynamics/mdFoam/mdFoam.C

...buoyantBoussinesqPimpleFoam/buoyantBoussinesqPimpleFoam.C

...buoyantBoussinesqSimpleFoam/buoyantBoussinesqSimpleFoam.C

...vers/heatTransfer/chtMultiRegionFoam/chtMultiRegionFoam.C

...nFoam/chtMultiRegionSimpleFoam/chtMultiRegionSimpleFoam.C