Tagits: favicon and app icons

Put these files at the root of the website, then add these lines inside <head>:

<link rel="icon" href="/favicon.ico" sizes="32x32">
<link rel="icon" href="/favicon.svg" type="image/svg+xml">
<link rel="apple-touch-icon" href="/apple-touch-icon.png">
<link rel="manifest" href="/site.webmanifest">

favicon.ico holds 16, 32 and 48 pixel sizes for older browsers. icon-maskable-512.png keeps the mark
inside the safe circle Android crops to.
