Add initial stats for v4 synthetic tree.
Add initial stats for v4 synthetic tree.

See inline comments for sources used. NOTE that this does not yet
include proper tallies, which will need to be obtained from the data
download (see my prior notes). Addresses #833.

OpenTreeOfLife/opentree,OpenTreeOfLife/opentree,OpenTreeOfLife/opentree,OpenTreeOfLife/opentree,OpenTreeOfLife/opentree,OpenTreeOfLife/opentree