PERF: don't render composer until we need it

app/assets/javascripts/discourse/controllers/composer.js.es6

@@ -465,6 +465,11 @@ export default DiscourseController.extend({
 
   canEdit: function() {
     return this.get("model.action") === "edit" && Discourse.User.current().get("can_edit");
-  }.property("model.action")
+  }.property("model.action"),
+
+  visible: function() {
+    var state = this.get('model.composeState');
+    return state && state !== 'closed';
+  }.property('model.composeState')
 
 });

app/assets/javascripts/discourse/templates/composer.hbs

@@ -1,3 +1,4 @@
+{{#if visible}}
 <div class='composer-loading'>
   {{loading-spinner}}
 </div>
@@ -116,3 +117,4 @@
 
   </div>
 </div>
+{{/if}}