Initialise component state in init() instead of constructor

This allows component state to be overridden via monkey-patch. ref #246

js/forum/src/components/PostStream.js

@@ -15,10 +15,8 @@ import ReplyPlaceholder from 'flarum/components/ReplyPlaceholder';
  * - `discussion`
  * - `includedPosts`
  */
-class PostStream extends mixin(Component, evented) {
-  constructor(...args) {
-    super(...args);
-
+class PostStream extends Component {
+  init() {
     /**
      * The discussion to display the post stream for.
      *
@@ -585,4 +583,6 @@ class PostStream extends mixin(Component, evented) {
  */
 PostStream.loadCount = 20;
 
+Object.assign(PostStream.prototype, evented);
+
 export default PostStream;