Make Pinbox a Progressive Web App

[msp301]

It would be good to look into making Pinbox a Progressive Web App (PWA) so it has a good user experience.

If any changes need to be made it would be better to get that done sooner rather than later.

[msp301]

Have merged first pass into master.
Running Lighthouse audit in Chrome DevTools on Pinbox production build achieves scores of:

• Performance: 50
• Accessibility: 88
• Best Practises: 93
• SEO: 89

TODO:

• Identify a way to reduce main thread workload
• Reduce DOM size taken up email list