Increase Interpretability of Signature Interpretation Figure

[gwaybio]

On a call today @mekelley and @ayberman noted that the signature interpretation figure is difficult to interpret - and I agree! Before publication we will need to clean it up to increase interpretability.

Let's use this issue to brainstorm how to improve the figure:

[gwaybio]

In broadinstitute/cell-health#124 (a different project) I extend the idea of the figure above. This update includes many of the recommendations we discussed on the call today.