DEV: select-kit 2 (#7998)

This new iteration of select-kit focuses on following best principales and disallowing mutations inside select-kit components. A best effort has been made to avoid breaking changes, however if you content was a flat array, eg: ["foo", "bar"] You will need to set valueProperty=null and nameProperty=null on the component.

Also almost every component should have an `onChange` handler now to decide what to do with the updated data. **select-kit will not mutate your data by itself anymore**

test/javascripts/acceptance/topic-notifications-button-test.js.es6

@@ -26,7 +26,7 @@ QUnit.test("Updating topic notification level", async assert => {
   await notificationOptions.selectRowByValue("3");
 
   assert.equal(
-    notificationOptions.selectedRow().name(),
+    notificationOptions.header().label(),
     "Watching",
     "it should display the right notification level"
   );