Bring airbnb/trebuchet to parity with devpuppy/trebuchet

It's time to get the last couple years of development back into the main repo.

Because of some past complexities that led to no common commit ancestor between the two, I did the version control equivalent of a "whole-body transplant" on the patient.  If you look at the commit history, it's actually very complete. There's just basically a Cretaceous–Paleogene extinction event, followed by all your favorite dinosaurs reappearing with colorful feathers.