This tab doesn't really provide anything useful, and can be quite
confusing in some cases. Each plugin is already listed below, and
you can navigate to their settings from there. We want to move away
from the catch-all Plugins category for site settings. Core plugins are
not shown in this list as at 97a812f022.
Previously if a specific plugin route was not available (e.g. there was an error loading the plugin's JS due to an ad blocker), the entire page would fail to load. This commit updates the behavior to catch this kind of issue and display a user-friendly message at the top of the screen.
