Update Chem Softening for Stability and Flowsheet Use

[kurbansitterley]

A few issues should be fixed after troubleshooting for KBHDP case study:

• adding isobaric constraints for waste and effluent
• adding isothermal constraints for waste and effluent
• use Expr_if in eq_CO2_first_basin
  • if total concentrations of Mg and Ca (as CaCO3) are higher than alkalinity, you will get negative CO2 required. This Expr_if will remedy this.
• fix a few errors where e.g., Ca as CaCO3 was used when it was supposed to be Ca Hardness
• convert some of Sharma costing equations to C = A*x**b where necessary/appropriate
• cost per reactor, then multiply by number of reactors (mixer and floc)

[kurbansitterley]

still need to update the test for modified costing equations.

[MuktaHardikar]

Approving pending issues:

1. Add outlet alkalinity calculation
2. Add method to select softening procedure based on inlet composition

[kurbansitterley]

Approving pending issues:

1. Add outlet alkalinity calculation
2. Add method to select softening procedure based on inlet composition

Memorialized this in #129 so it doesn't get buried.