Use norm of permeability tensor as weight

To get a scalar rel.perm. in the end, use the Frobenius norm of the
abs.perm. as weights instead of the full tensor.
Abs. perm. weights for each block in column
fixup! Compute volume fractions and depth fractions used as weights
fixup! Compute volume fractions and depth fractions used as weights
Get rel. perm. for one mobile phase but the other present

There is always connate brine left in the CO2 phase, and there is
CO2 in the parts where the plume has been but is not anymore. These
will be impedients for the phase that is left, and we must know the
scaling factor (rel.perm.) that must be used to account for that.