Generalize CatalyticWall boundary condition to handle different number of reactants and products

[pbauman]

We assume the same number of reactants and products and use that assumption in several places. We need to remove it. The main thing is that means we have to rely on the user supplying the gamma value for each of the terms. This becomes error prone in the single reactant, single product case since the gamma there is specified in terms of one of the reactions and you use "minus" to get the value of the other corresponding guy. Would be good to have that functionality automatically since I already screwed up trying to convert the gamma by hand in initial testing and lost mass conservation...