Webpack (#33)

See https://github.com/flarum/core/pull/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"
* Restructure `less` directory

extensions/mentions/js/src/forum/addPostReplyAction.js

@@ -0,0 +1,22 @@
+import { extend } from 'flarum/extend';
+import Button from 'flarum/components/Button';
+import CommentPost from 'flarum/components/CommentPost';
+
+import reply from './utils/reply';
+
+export default function () {
+  extend(CommentPost.prototype, 'actionItems', function (items) {
+
+    const post = this.props.post;
+
+    if (post.isHidden() || (app.session.user && !post.discussion().canReply())) return;
+
+    items.add('reply',
+      Button.component({
+        className: 'Button Button--link',
+        children: app.translator.trans('flarum-mentions.forum.post.reply_link'),
+        onclick: () => reply(post)
+      })
+    );
+  });
+}