Added hexo-pwa capabilities to the theme

[marcofranssen]

This change adds PWA capabilities to the theme when using the hexo-pwa plugin.

Extract from my _config.yaml

pwa:
  manifest:
    path: /manifest.json
    body:
      name: Marco Franssen blog
      short_name: Marco F blog
      start_url: .
      description: Blog by Marco Franssen, covering software development!
      theme_color: "#006bde"
      background_color: "#ffffff"
      display: standalone
      icons:
        - src: images/icons/icon-72x72.png
          sizes: 72x72
          type: image/png
        - src: images/icons/icon-96x96.png
          sizes: 96x96
          type: image/png
        - src: images/icons/icon-128x128.png
          sizes: 128x128
          type: image/png
        - src: images/icons/icon-144x144.png
          sizes: 144x144
          type: image/png
        - src: images/icons/icon-152x152.png
          sizes: 152x152
          type: image/png
        - src: images/icons/icon-192x192.png
          sizes: 192x192
          type: image/png
        - src: images/icons/icon-384x384.png
          sizes: 384x384
          type: image/png
        - src: images/icons/icon-512x512.png
          sizes: 512x512
          type: image/png