Speed up build/compilation

The current build time is extremely slow and will grow as the codebase does. I'm not as concerned with the production build time as I am about the incremental builds for hot module reloading since that's what impacts DX most, but I'd expect both to be improved with some of the following solutions.

There's a few things we can try:

• HappyPack
• Webpack DLL Plugin
• Use babel-preset-node6 for server bundle

Some helpful reads/links:

• Webpack issue with a lot of good thoughts: https://github.com/webpack/webpack/issues/1574#issuecomment-189580065
• Blog post on using DLL plugin
• SlideShare on making webpack builds 10x faster

I'm sure there's a handful of other levers we could pull, please feel free to add more info!

I'm going to start by implementing these in our internal project first and then seeing how we can cleanly abstract this upstream into kyt. But individual PRs are welcome!