Build icons src relative to manifest location

[emmercm]

Icon src in the manifest is defined relative to the manifest location, this doesn't get carried into the generated tags.

Example file at /.../manifest/v4/manifest.json (path and data obfuscated for security):

{
   // ...
   "icons": [
      {
         "src": "mobile-icon-76.png",
         "sizes": "76x76",
         "type": "image/png"
      },
      {
         "src": "mobile-icon-120.png",
         "sizes": "120x120",
         "type": "image/png"
      },
      {
         "src": "mobile-icon-152.png",
         "sizes": "152x152",
         "type": "image/png"
      },
      {
         "src": "mobile-icon-180.png",
         "sizes": "180x180",
         "type": "image/png"
      },
      {
         "src": "mobile-icon-192.png",
         "sizes": "192x192",
         "type": "image/png"
      }
   ]
}

Generates:

<link rel="apple-touch-icon" sizes="152x152" href="mobile-icon-152.png">
<link rel="apple-touch-icon" sizes="120x120" href="mobile-icon-120.png">
<link rel="apple-touch-icon" sizes="76x76" href="mobile-icon-76.png">
<link rel="apple-touch-icon" sizes="60x60" href="undefined">
<link rel="apple-touch-icon" sizes="57x57" href="undefined">
<link rel="apple-touch-icon" sizes="72x72" href="undefined">
<link rel="apple-touch-icon" sizes="114x114" href="undefined">
<link rel="icon" sizes="128x128" href="undefined">
<link rel="icon" sizes="192x192" href="mobile-icon-192.png">