Email notification template GUI complains about %{base_url}

@pfaffman This is still not fixed even in 3.2.1. Nothing changed since my initial report. Could this be bumped up to get fixed, please? In short, pretty much EVERY template should allow %{base_url} given that %{url} only includes the path after the base url.

At the very least don’t prevent the user from using it (despite it not showing in the list of available keys).