Enabling PWA

[lily-gh]

What

This PR enables Large Type to function as a Progressive Web App and be installed on mobile phone's home screens.

Why

I've found Large Type to be really useful when giving your phone number or address at hotel receptions or doctor clinics, so I looked for a way to make it even easier to use it on the phone by turning it into a PWA that can be added to the phone home screen.

How

Icons for the home screen and splash screen were generated via PWA asset generator

When first opening Large Type on the phone, the CSS and JS files will be cached, and after that the app can also be used without internet connection.

Chrome Lighthouse Report

Using Large Type offline on iPhone