Improving comments in phasor dynamics to emphasize better TODO items

[pelesh]

Description

Adding more verbose TODO comments.

Proposed changes

Adding comments that mark places in the code where some immediate actions needs to be taken in order to implement JSON parser and automate system model assembly directly from the input file.

Checklist

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

Further comments