Update to apply a final filtering to the Q estimate

Previously, our Q estimates were not constrained to force mass
conservation: mass conservation was used as a constraint to estimate A0
& n, but not to force mass conservation a posteriori. I added a simple
Kalman-filter type post-process step (FilterEstimate.m) where that is
taken care of. Q uncertainties typically don't improve much, but we
have answers that make more sense!