Fixed DiffusionSolver and Reaction Diffusion solvers. BEfore on hex lattice with no fluxc boundary conditions solvers were leaking chemical. I fixed how boundary cionditions are calculated for both hex and Cartesian lattice. There si an opportunity to improve performance a but here by getting rid of boundaryConditionInit function but this is really minor stuff. I leave it for now because when periodic BCs are used this function is still needed. I will get rid of this fcn in the next code iteration