Webpack (#1367)

* Replace gulp with webpack and npm scripts for JS compilation
* Set up Travis CI to commit compiled JS
* Restructure `js` directory; only one instance of npm, forum/admin are "submodules"
* Refactor JS initializers into Application subclasses
* Maintain partial compatibility API (importing from absolute paths) for extensions
* Remove minification responsibility from PHP asset compiler
* Restructure `less` directory

js/src/forum/components/ReplyPlaceholder.js

@@ -0,0 +1,72 @@
+/*global s9e*/
+
+import Component from '../../common/Component';
+import avatar from '../../common/helpers/avatar';
+import username from '../../common/helpers/username';
+import DiscussionControls from '../utils/DiscussionControls';
+
+/**
+ * The `ReplyPlaceholder` component displays a placeholder for a reply, which,
+ * when clicked, opens the reply composer.
+ *
+ * ### Props
+ *
+ * - `discussion`
+ */
+export default class ReplyPlaceholder extends Component {
+  view() {
+    if (app.composingReplyTo(this.props.discussion)) {
+      return (
+        <article className="Post CommentPost editing">
+          <header className="Post-header">
+            <div className="PostUser">
+              <h3>
+                {avatar(app.session.user, {className: 'PostUser-avatar'})}
+                {username(app.session.user)}
+              </h3>
+            </div>
+          </header>
+          <div className="Post-body" config={this.configPreview.bind(this)}/>
+        </article>
+      );
+    }
+
+    const reply = () => {
+      DiscussionControls.replyAction.call(this.props.discussion, true);
+    };
+
+    return (
+      <article className="Post ReplyPlaceholder" onclick={reply}>
+        <header className="Post-header">
+          {avatar(app.session.user, {className: 'PostUser-avatar'})}{' '}
+          {app.translator.trans('core.forum.post_stream.reply_placeholder')}
+        </header>
+      </article>
+    );
+  }
+
+  configPreview(element, isInitialized, context) {
+    if (isInitialized) return;
+
+    // Every 50ms, if the composer content has changed, then update the post's
+    // body with a preview.
+    let preview;
+    const updateInterval = setInterval(() => {
+      const content = app.composer.component.content();
+
+      if (preview === content) return;
+
+      preview = content;
+
+      const anchorToBottom = $(window).scrollTop() + $(window).height() >= $(document).height();
+
+      s9e.TextFormatter.preview(preview || '', element);
+
+      if (anchorToBottom) {
+        $(window).scrollTop($(document).height());
+      }
+    }, 50);
+
+    context.onunload = () => clearInterval(updateInterval);
+  }
+}