This commit contains a few improvements:
* Use LinkTo instead of a button with a weird action referencing the
controller to navigate to the filtered settings for a plugin
* Add an AdminPlugin model with tracked properties and use that when
toggling the setting on/off and in the templates
* Make it so the Settings button for a plugin navigates to the correct
site setting category instead of always just going to the generic
"plugins" one if possible
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.
