cli: make phylogeny a new sub-command

[ktmeaton]

In other analysis projects, I'm wishing for the recombination-aware phylogenetic methods I've written here. Pretty much all the functions, but primarily these:

• phylogeny::get_common_ancestor
• phylogeny::get_ancestors
• phylogeny::get_descendants
• phylogeny::get_recombinants

There might be value in creating a new subcommand rebar phylogeny so that we can do things like:

1. rebar phylogeny --graph phylogeny.json --mrca XE,XG