NPM (Yarn) modules are now vendored

[Nikhil Benesch]

The days of NPM registry errors failing our builds are behind us!* Much like our Go dependencies, our JavaScript dependencies are now checked in to a submodule that lives at pkg/ui/yarn-vendored.

I'm expecting this transition to go smoothly, but please be on the lookout for any UI build related issues in the next few days.

If you find yourself with untracked submodules, usually because you checked out a branch that predates a given submodule:

    $ git clean -ffd

Note the extra -f. If you find yourself with submodules that are stuck on the wrong commit:

    $ git submodule update -f --recursive

Nikhil

*Please find some wood to knock on after reading this message.