The `specialSeparationDims` list is hard to maintain

[ToddFincannonEI]

EPS has an ongoing need to use the specialSeparationDims section in the spec file. The current format of this section requires listing every variable that needs to be separated to avoid a cyclic dependency condition. Maintaining that list is an error-prone process, because affected variables come and go as the model is developed.

[chrispcampbell]

See PR #602 for details on the proposed solution.