Contents of mutation popup

[hyanwong]

@kitchensjn in #103 said:

One thing that I've changed is I've separated the "label" text from the "content" of the popup. This allows for things like the condense mutation labelling scheme (x2, x4, etc). Both of these are generated on draw(), which limits the current customizability. We could store it in the mutations data frame (similarly to the labels for nodes in the nodes data frame). Users could then do customize this to their liking, but this strategy may not play nicely with condense_mutations=True if the user has added a lot of text to the mutation "content" and then all of this text gets merged together into a single popup. I think I'll save this added customizability to mutations for the next release (v0.0.4).

It would indeed be useful to have different "content" strings in the "popup" mutation box / list, which could be longer, e.g. "T->C @ pos 101, 34.2 generations". It's unclear exactly how best to make this flexible, however.