Add proper icons + manifest

[slaFFik]

So when the site is added in Chrome to a Desktop a link, that opens an "app" (Chrome tab separately without tabs interface). This shortcut in Start menu on Windows10 doesn't have own icon (Chrome icon is used).

[GaryJones]

Chrome doesn't seem to have any icon at all now.

I can recommend http://realfavicongenerator.net/ for generating all of the correct icons.

[slaFFik]

I think I will create a PWA from this source. That's what I really want to do in June.