for enthalpy and internal energy respectively

Change the implementation of alphah and alphae to use the local heat capacity
rather than attempting to compensate for the variation in an ad hoc manner.  For
correctness a heat capacity gradient term should be added to the energy
equations.

Replaced lduMatrix::solverPerformance with SolverPerformance<scalar>

LduMatrix: coupled solvers are now run-time selectable for solving fvMatrices by conversion of the fvMatrix/lduMatrix to LduMatrix