Move PowerSystemsData.hpp and CircuitGraph.hpp to correct subdirectories

[pelesh]

Description

• Move PowerSystemsData.hpp -> src/Model/PowerFlow.
• Move CircuitGraph.hpp -> src/Model/PowerElectronics.
• Separated Matpower parser from FileIO.hpp as it is needed only for power flow models.
• Remove unnecessary include directives

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

Proposed changes

PowerSystemsData.hpp is used only by power flow and experimental models. It is specific to Matpower input data and will not be used for phasor domain dynamics models.

CircuitGraph.hpp is used only for power electronics models.

Most of the models do not need to include either of the two header files.

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

[pelesh]

CC @superwhiskers

[nkoukpaizan]

The changes look good to me. Tests pass in CI and on Frontier.