Update webpack and other modules (faster builds) and add live-rebuild…

Created by: ktiedt

… support for dev - #1327 (closed)

This bumps up the versions for webpack (massive perf increases in some cases) and our other libraries, initial testing looks solid. Did not test on Heroku.

This also adds yarn run start:dev which will spin up a dev server + watch the files webpack is minifying to rebuild as files are changed.