Custom message when content not found

[JayJohnsonWashoeCounty]

Once I have deleted a dashboard, the error message that a user who has perhaps bookmarked that site sees is not very friendly:

It would be much better to allow me to provide a nicely worded, organization-specific message, with perhaps a link to our OpenData site or some other page with GIS content.  This is not only a dead-end, but it is not visually attractive...

Anyway, we need a better way to manage "retired" content.

Jay