ENH: When clicking on a tip, show all mutations at that tip

[corneliusroemer]

I don't think it's possible to see all mutations at a tip at the moment. One needs to traverse the branch.

This is unfortunate. It would be amazing to be able to click and see all mutations leading up to a tip or branch - just as one can see the mutations that are happening just on the branch itself.

I want to quickly see: what spike mutations are up to here? This is hard to answer currently I think.