Revise 404 page: Credentials not found

[alexfigtree]

Users land on a 404 page that is not helpful. Current page does not explain why a user would land there.

We want to make the 404 page (seen here, for example: https://verifierplus.org/credentials/32ba477d-07d4-4054-8401-c9c40e7235fa) friendlier and more helpful. Instead of saying "404 credential not found", we could say something more like:

"Credential Not Found: Credential has likely expired or has been unshared by a user"

Open to thoughts on a visual re-design.

[gwalsh311]

Suggestion:

404: Credential Not Found

Please confirm you have entered the correct URL or public link. Other reasons for this error could include:

• the credential has expired
• the credential holder has unshared the URL or public link

[kayaelle]

I don't think we're showing a 404 page - when I click on a link that I've unshared, it just says "loading"....

Upping priority so we can depend on messaging when we add QR code to PDF.