Webpack (#14)

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/lock/less/forum.less

@@ -0,0 +1,7 @@
+.DiscussionLockedPost {
+  .EventPost-icon,
+  .EventPost-info,
+  .EventPost-info a {
+    color: #888;
+  }
+}