Not installable as web app when using login credentials

[PoW-chain]

When I require credentials to login to the explorer, it is not installable as web app. The reason is the manifest file is then not loaded correctly.

When using credentials, crossorigin="use-credentials" should be added to the manifest link in the layout.pug, as such:
link(rel="manifest", href=./img/network-${network}/site.webmanifest, crossorigin="use-credentials")

Also I noticed the manifest files do not include "start_url", which is required according to the specification.

I fixed this manually in my installation and fixed the issue. Don't know how to create the pull request for this.