different implementation of signal assignment

[superwhiskers]

another attempt at implementing signal assignment on components

closes #190

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.

[shakedregev]

This code requires the user to memorize relations between enums and integers. There are multiple problems with type safety. I recommend improving #193 instead.

[pelesh]

Branch is not the best example to work this out because a branch does not have signal connections. I would use generator and governor as my two test cases.

[superwhiskers]

closing in favor of #193