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
Martin Brennan
Isaac Janzen
David Taylor
Robin Ward