Update front-end development workflow

[jwhitlock]

User story

As a front end developer, I want a better integrated development environment by the end of 2018, so that I can more rapidly make changes.

Acceptance criteria

• Goal: There is one place to add and update front-end tools (bug 1468491: Update node 8, dependencies kuma#4852)
• Goal: No host installs are required for front-end development except for Docker
• A node-based tool chain, not django-pipeline, is used to process assets (see bug 1380419, Taiga US 1799
• Assets continue to have unique names based on contents and long cache lifetimes
• Front-end development documentation is up-to-date

[tobinmori]

Closing because this is old.