Should add manifests

[geoffreyyip]

• User can be prompted to Install the Web App
  Failures: No manifest was fetched, Site does not register a Service Worker, Manifest start_url is not cached by a Service Worker.
• Configured for a custom splash screen
  Failures: No manifest was fetched.
• Address bar matches brand colors
  Failures: No manifest was fetched, No <meta name="theme-color"> tag found.
• Manifest's short_name won't be truncated when displayed on homescreen
  Make your app's short_name less than 12 characters to ensure that it's not truncated on homescreens.

Should add a manifest to implement some mobile friendly features.