Feature: Support git branch installs all the way through `init/package.json` dependencies expansion.

[ryan-roemer]

• Support a way to do "proxy through the git branch I'm installing from" for actual prod and dev deps. (Dev is potentially harder because of git and /dev/ directory).
  • This is complicated by a wontfix npm feature request for support for this: Allow subdirectories within git repos in npm install  npm/npm#2974