Move topic list extensibility to `topic-list` component

app/assets/javascripts/discourse/components/topic-list-item.js.es6

@@ -52,7 +52,8 @@ export default Ember.Component.extend(bufferedRender({
       classes.push('has-excerpt');
     }
 
-    _.each(['liked', 'archived', 'bookmarked'],function(name) {
+
+    ['liked', 'archived', 'bookmarked', 'pinned'].forEach(name => {
       if (topic.get(name)) {
         classes.push(name);
       }

app/assets/javascripts/discourse/components/topic-list.js.es6

@@ -5,6 +5,9 @@ export default Ember.Component.extend({
   classNames: ['topic-list'],
   showTopicPostBadges: true,
 
+  // Overwrite this to perform client side filtering of topics, if desired
+  filteredTopics: Ember.computed.alias('topics'),
+
   _init: function(){
     this.addObserver('hideCategory', this.rerender);
     this.addObserver('order', this.rerender);

app/assets/javascripts/discourse/controllers/discovery/topics.js.es6

@@ -25,9 +25,6 @@ const controllerOpts = {
     this.setProperties({ order: "default", ascending: false });
   },
 
-  // Overwrite this to perform client side filtering of topics, if desired
-  filteredTopics: Ember.computed.alias('model.topics'),
-
   actions: {
 
     changeSort(sortBy) {

app/assets/javascripts/discourse/templates/components/topic-list.hbs

@@ -14,8 +14,20 @@
       bulkSelectEnabled=bulkSelectEnabled}}
   </thead>
 {{/unless}}
+
+{{plugin-outlet
+  name="before-topic-list-body"
+  args=(hash
+    topics=topics
+    selected=selected
+    bulkSelectEnabled=bulkSelectEnabled
+    lastVisitedTopic=lastVisitedTopic
+    discoveryList=discoveryList)
+  tagName=""
+  connectorTagName=""}}
+
 <tbody>
-  {{#each topics as |topic|}}
+  {{#each filteredTopics as |topic|}}
     {{topic-list-item topic=topic
                       bulkSelectEnabled=bulkSelectEnabled
                       showTopicPostBadges=showTopicPostBadges

app/assets/javascripts/discourse/templates/discovery/topics.hbs

@@ -32,12 +32,6 @@
   {{/if}}
 
   {{#if hasTopics}}
-
-    {{plugin-outlet
-      name="discovery-before-topic-list"
-      tagName=""
-      args=(hash model=model category=category)}}
-
     {{topic-list
       highlightLastVisited=true
       top=top
@@ -54,7 +48,8 @@
       expandGloballyPinned=expandGloballyPinned
       expandAllPinned=expandAllPinned
       category=category
-      topics=filteredTopics}}
+      topics=model.topics
+      discoveryList=true}}
   {{/if}}
 {{/discovery-topics-list}}