extract equilibrium Cs and Cl from CALPHAD

Previous values of Cse, Cle represented minima of the pure phase
free energy curves, a critical error that under-reports the true
values required by equal chemical potential in each phase -- as
represented by the common tangent construction. The new values
come from equilibrium calculations using PyCALPHAD, and represent
the true solidus and liquidus values at 1550K.

Author: Trevor Keller