FIX: Fully re-render ads when navigating between pages (#188)

In the past, the ad plugin relied on two side-effects to achieve this behaviour:

1. Components being fully destroyed/rendered when navigating between pages. This stopped working when Discourse core moved to the more efficient 'loading slider' UI

2. The `listLoading` argument. This was an implementation detail of the old discovery routing infrastructure. Core recently overhauled this and removed the `listLoading` argument, because loading is now handled properly by the Ember router.

Instead of these two properties, we can use the `currentRoute` property of Ember's router service to trigger changes when navigating between pages. A common `{{#each` trick is used to fully destroy/re-render components even if the ad network is unchanged.

test/javascripts/acceptance/house-ad-test.js

@@ -2,6 +2,7 @@ import { visit } from "@ember/test-helpers";
 import { test } from "qunit";
 import {
   acceptance,
+  query,
   updateCurrentUser,
 } from "discourse/tests/helpers/qunit-helpers";
 
@@ -69,12 +70,21 @@ acceptance("House Ads", function (needs) {
     assert
       .dom(".h-topic-list")
       .exists({ count: 1 }, "it should render ad above topic list");
+    const originalTopAdElement = query(".h-topic-list");
 
-    await visit("/latest");
     assert
       .dom(".h-between-topic-list")
       .exists({ count: 5 }, "it should render 5 ads between topics");
 
+    await visit("/top");
+    const newTopAdElement = query(".h-topic-list");
+
+    assert.notStrictEqual(
+      originalTopAdElement,
+      newTopAdElement,
+      "ad is fully re-rendered when changing pages"
+    );
+
     await visit("/t/28830");
 
     assert