instead of laplacian(alpha, h). This is necessary when Cp is not uniform.

ENH: Adding useChemistrySolver in reactingOneDim solid region to avoid using chemistry solvers in reacting solids
     Adding non const access function to chemistryModel.H for combustion models that calculates RR externally
     Removing EulerImplicit from options in solidReactions.
BUG: Correcting function used by sequential solver in pyrolysisChemistryModel.C