Have consensus function record blen info

[eaton-lab]

Consensus tree function should not only record consensus topology and get support but could also get branch length information. This is a bit complicated and their are different methods for how to summarize lengths given their interdependency (e.g., marginalized values). Best to implement something simple first, but default for now will remain setting edge lengths to 1 to make it clear that edge length info was dropped during consensus.