Performance audit

[mwistrand]

Enhancement

After #68 is resolved, we should run a performance audit and look for ways to decrease the build time. @matt-gadd has already noted a few possible enhancements, such as using experimentalWatch on the ts-loader and adding caching plugin like https://github.com/mzgoddard/hard-source-webpack-plugin.

Package Version: 4+

[maier49]

I tested the hard source caching plugin and as expected it significantly improved repeated build times. I've opened a PR to add that to the build. My testing with the experimentalWatchApi for ts-loader didn't show any improvements in build time when watching. The only other low hanging fruit I saw was removing the postCss loader when it's not needed but we are already doing that when the experimental speed flag is set.