Implement yarn

[dgreene-r7]

This PR adds a yarn.lock file so we can use Yarn to deterministically install our dependencies.

It also deprecates node-libuuid in favor of uuid so we don't have to deal with C bindings.

[coveralls]

Coverage remained the same at 92.739% when pulling 4ad6900 on implement-yarn into 01b40a7 on master.

[fmitchell-r7]

@dgreene-r7, how does the yarn.lock file get generated?

[dgreene-r7]

yarn install.

It's backwards compatible with npm so we're not losing any functionality; only gaining the ability to deterministically install dependencies.