Upgrade to webpack v3

Webpack v3 has been released with support for partial scope hoisting. It has the potential to reduce code size as well as improve execution time by greatly reducing the number of unnecessary nested closures.

• install webpack v3 in new branch, ensure no migration changes are needed
• configure and enable scope hoisting
• compare frontend asset file sizes
• compare frontend performance through Google DevTools on various pages against a baseline taken from our pre-webpack 3 assets