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

framework/core/views/frontend/app.blade.php

@@ -30,6 +30,7 @@
     @if ($allowJs)
       <script>
         document.getElementById('flarum-loading').style.display = 'block';
+        var flarum={extensions:{}};
       </script>
 
       @foreach ($jsUrls as $url)
@@ -41,16 +42,7 @@
         @if (! $debug)
         try {
         @endif
-          var app = System.get('flarum/app').default;
-          var modules = {!! json_encode($modules) !!};
-
-          for (var i in modules) {
-            var module = System.get(modules[i]);
-            if (module.default) module.default(app);
-          }
-
-          app.boot(@json($payload));
-
+          flarum.core.app.boot(@json($payload));
         @if (! $debug)
         } catch (e) {
           window.location += (window.location.search ? '&' : '?') + 'nojs=1';