Investigate using service workers to allow app to work offline

[taesungh]

To make this website/tool more portable for users, service workers can be configured to allow the site to run offline (when not connected to the internet). Once the app is loaded, everything runs locally, and none of the features need an active internet connection. This is also related to making this available as a progressive web app (PWA) where a user can "install" the site as an app (e.g. Add to home screen, or Add to Dock).