Enumerate authors missing nodes and edges in neurotree

[stripathy]

Which neuroelectro authors are missing neurotree nodes?
Which neuroelectro authors have neurotree nodes missing appropropriate edges?

[stripathy]

@svdavid , I've implemented a first version of this analysis, focusing on only authors who have published a paper on CA1 Pyramidal cells. Results in this csv: https://github.com/neuroelectro/neuroelectro_neurotree/blob/master/ca1_pyr_auths.csv

Unique last authors publishing on CA1 pyramidal cells in NeuroElectro: 68
with NeuroTree nodes: 44
with paths to other CA1 author nodes: 36-38

Generalizing from this, we can expect that about half of the NeuroElectro authors will have useful lineage data in NeuroTree in its current state.

Comments:

1. I'm relying on neurotree's function to return an author node given a pmid as input.
2. The "Connectedness" measure is the ratio of how often I can find a path between an author and the other CA1 authors.
3. It's simple enough to implement this for all authors, it'll just take a while since I need to query the path length for each author-pair.