Compare different systems/targets in a single plot

[ijpulidos]

It might be useful to compare different graphs and/or systems in a single plot. Say for example you want to compare two different force fields compare to each other in a range of targets (not just a single one). Imagine comparing espaloma vs openff in all the targets of some protein-ligand-benchmark.

Right now we don't have an easy way to do this comparison from the cinnabar objects, I wonder if we want to include this capability in the future, such that we can extract the points from the plot that would be generated for each target (in x-y pairs or similar) from cinnabar objects and just merge them together to create a single plot with the information of different targets.