Progressive web app example

Exploring new and some not so new features of browser

Features

Add firebase constants (firebase Project ID and firebase cloud functions plublic url) in /public/src/js/config.js and /functions/config.js
Make in /functions/ make two files: pwagram-fb-key.json and pwagram-vapid-key.json, first containing firebase private key and second one containing vapid key (https://github.com/web-push-libs/web-push)
In /functions/ folder run npm install and than npm run deploy to deploy firebase functions
In root folder run npm install
From same folder run npm run build and after that npm start