Plot average ancestor length in time and genome bins

[jeromekelleher]

We'd like a plot that summarises the distribution of ancestor lengths over time and along the genome.

The x axis is genome coordinates, binned in to N windows

The y axis is time, binned into K windows

We can the plot the average ancestor length as a colour intensity in this N x K matrix

See also #19

[jeromekelleher]

I guess ancestor length is something that we'd add to the node data table (#39)? It would be an ancestral_span or something?

[jeromekelleher]

This is something we'd add to the node panel I think all right, it's a property of the actual genomes.

[savitakartik]

There's an open PR for this: #68
Although, we were not sure if we wanted to include this feature, so I'm happy to keep it closed/revisit.

[benjeffery]

Ah! Sorry didn't realise. I'll reopen till we decide.