Fix ACP alerts to use same system as client (#6396)

* Fix PostCSS warning message

* Fix disconnect indicator styling

Would increase size of quick actions when active

* Use same alert system in ACP and client

- Remove snackbar
- Add styling and fix template for ACP (based on Persona)

src/meta/js.js

@@ -85,7 +85,6 @@ JS.scripts = {
 		'public/vendor/semver/semver.browser.js',
 		'public/vendor/jquery/serializeObject/jquery.ba-serializeobject.min.js',
 		'public/vendor/jquery/deserialize/jquery.deserialize.min.js',
-		'public/vendor/snackbar/snackbar.min.js',
 		'public/vendor/slideout/slideout.min.js',
 		'public/vendor/nprogress.min.js',
 	],