Consider adding sections for combinations of interfaces #9
Description
Strictly speaking many properties don't belong to a single phase but are only valid for pairs of phases.
Examples:
- For solidification problems, the interfacial energy (or Gibbs-Thomson coefficient) is between the solid and the liquid, it doesn't "belong" to either of the phases individually
- For eutectic solidification problems, the contact angles are related to both solid phases and the liquid. They only make sense in that context.
Adding sections for properties relating to interactions between two or three phases increases the complexity a bit, but lets us be more general. Is approach is inspired by what Brian Puchala did with CASM for uploading to Materials Commons.