HMWSoln: avoid recomputing lambdas if ionic strength hasn't changed.
MaskellSolidSolnPhase: Avoid recomputing activity coefficients if
r and T haven't changed.
Fix sign error in chemical potentials and update
activity coefficients accordingly.
Correct implementation of getActivityConcentrations()
Additional unit tests.
installShomateThermoFromXML now checks that
7 coefficients are supplied in the floatArray and
throws if that is not the case.
Also update MaskeLLSolidSolnPhase_Test xml files
to correctly contain 7 coefficients to not trigger
the newly added throw.
Based on Maskell, Shaw, and Tye, Electrochimica Acta 28(2) 225-230 1983.
Includes unit tests checking calculation of the chemical potential values
and parsing of the mixing enthalpy parameter from an XML file.
