Always add number of descendant samples

[hyanwong]

As discussed by Ana. Doesn't look great at the moment with large labels, so needs some tweaking:

[hyanwong]

We can actually remove the "samples" suffix by using the label hack I merged earlier:

sc2ts.sample_subgraph(712029, ts, treeinfo, 
    node_label_replace={
        "Unknown":"",
        "Unknown ":"",
        " samples": ""  ## Remove the word "samples"
    },
   ...
)
plt.show()

[jeromekelleher]

LGTM - @a-ignatieva what do you think?

[a-ignatieva]

Looks good! Thanks @hyanwong