Build Tools: Add npm package-lock.json for npm v5.x

This changeset adds support for npm 5 which include significant performance improvements, these are primarily due updated caching, offline caching and the addition of a package-lock.json to leverage the new caching.

To install and use npm 5 with your existing install of Node.js 6 or 7 run npm i npm@5 -g. Node.js 8 support will be added in a follow up ticket.

Installing npm modules for bbPress is now ~6x faster with npm 5 🏎

Fixes #3113.