Scaling, fix minor MCAS issue, and set up Seawater properties for dynamics

[dallan-keylogic]

Summary/Motivation:

As part of working on dynamics in WaterTap, I added material and energy density terms to the Seawater property package and made some improvements to unit model scaling.

Additionally, I found and fixed an issue when the MCAS property package was used 1) in a Feed block (and probably also Product block) when 2) using a time set with more than one element. The issue seems to have been caused because the state variables (either flow_mol_phase_comp or flow_mass_phase_comp depending on the configuration) were being created through the on-demand property framework, instead of creating them when initializing the state block. The fact that those state variables were not entirely initialized when the Feed block tried to create References to them at the unit-model level (moving the time index set from living on the state block to living on the state variable) caused an obscure Pyomo error.

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