Allow species in `yValues` of the visualization table

[paulflang]

Which problem would you like to address? Please describe.
Atm it seems like only observables can be plotted on the y axis. It would be nice to also be able to plot species.

Additional context
This would be helpful to visually check

• if the behavior of non-observed species for a given optimization result seems biologically reasonable
• how species differ between experimental conditions
• how species differ between different optimization results, etc.

[dweindl]

Agreed, this would be quite helpful. When changing that, we should probably just allow any model entity with globally unique identifier (e.g., parameters, compartments).

[dweindl]

I think for the current way of plotting based on simulation files we could allow for pretty much everything that is present in that file. It would be an abuse of observableId, though. For practical purposes, I think it would already work if you add your species to a simulation file and let libpetab plot it. There is currently no validation for simulation files.