Create phasor dynamics model data structures (take two)

[pelesh]

Description

Create data structures to store model data for each component model type, e.g. an electrical machine data structure. These data structures will contain a superset of parameters for each component model type.

@abirchfield @lukelowry @alexander-novo @reid-g @abdourahmanbarry

Proposed changes

The purpose of these data structures is to decouple data input from component models, so that:

• Multiple inputs (GUI, file input, etc.) can be used to enter system model data in GridKit.
• Multiple component model implementations can use the same data structures to instantiate the component.
• Analysis can be performed on these data structures to compute sparsity pattern of system Jacobian without even instantiating the component or system models.

The changes proposed in the PR are the first step in this direction.

Checklist

• All tests pass.
• Code compiles cleanly with flags -Wall -Wpedantic -Wconversion -Wextra.
• The new code follows GridKit™ style guidelines.
• There are unit tests for the new code.
• The new code is documented.
• The feature branch is rebased with respect to the target branch.

Further comments