Adds PWA manifest and icons, template updates.

[noahlange]

What does this do?

Adds a PWA manifest and icons. I made additional changes to the header template and .gitignore file to add the appropriate <link /> tag and un-ignore the manifest.

I generated crop dimensions for the icons using smartcrop.js and compressed with pngquant.

Is there a GitHub Issue that this is resolving?

Yes, it's a start on #454. We'll need to create a service worker before it can be closed, however.

[Glinkis]

I'm not entirely familiar with how PWAs work but don't we need to genenerate a list of all the app files?

[noahlange]

I'm not entirely familiar with how PWAs work but don't we need to generate a list of all the app files?

According to Google, the only other thing that's mandatory is a service worker—Chrome didn't indicate there were any other issues when I opened the application panel in the dev tools.

[ryceg]

What's the state of this? Are we shelving the PWA for the moment?

[noahlange]

I dunno, and I'm not entirely sure what a proper service worker entails.

[ryceg]

Haha! Righto, guess this one will just sit on the backburner while we wait for somebody with a bit more know-how to show us how it's done :)