Move current admin footer reminder when running development version to Site Health

[knutsp]

When running a development version, there is a text in the right admin footer like this: "You are using a development version %(version)s. Cool! Please stay updated."

This is really information that fits Site Health. It's also in the line of de-emphasizing version in the admin.

Site Health could also need a "cool" category, but going along with a gentle warning that such is not safe for production.