Compile `.es6.js` files with Traceur
Revert "Compile `.es6.js` files with Traceur"

This reverts commit fe8048200c037226f7f5f97e3463083635e7f928.

Can't get this Traceur loader to work. Not sure if it's an issue with
Traceur or the loader, but going to remove this loader and try a
different one to see.
Use `webpack-traceur-loader` for ES6 features

Couldn't get `traceur-loader` to work, but `webpack-traceur-loader`
seems to work great!

This enables ES6 features on files ending in `.es6.js`.
Merge branch 'enable-es6-javascript-features'