Rework extension bootstrapping

System JS modules don't execute when they're registered, so we need to
import them explicitly. While we're at it, we may as well make the
locale bootstrapper a module too.

stubs/extension/src/Extension.php

@@ -0,0 +1,27 @@
+<?php namespace {{namespace}};
+
+use Flarum\Support\Extension;
+use Illuminate\Events\Dispatcher;
+
+class Extension extends BaseExtension
+{
+    /**
+     * Bootstrap the application events.
+     *
+     * @return void
+     */
+    public function boot(Dispatcher $events)
+    {
+        $events->subscribe('{{namespace}}\Listeners\AddClientAssets');
+    }
+
+    /**
+     * Register the service provider.
+     *
+     * @return void
+     */
+    public function register()
+    {
+        //
+    }
+}

stubs/extension/src/Listeners/AddClientAssets.php

@@ -0,0 +1,33 @@
+<?php namespace {{namespace}}\Listeners;
+
+use Flarum\Events\RegisterLocales;
+use Flarum\Events\BuildClientView;
+use Illuminate\Contracts\Events\Dispatcher;
+
+class AddClientAssets
+{
+    public function subscribe(Dispatcher $events)
+    {
+        $events->listen(RegisterLocales::class, __CLASS__.'@addLocale');
+        $events->listen(BuildClientView::class, __CLASS__.'@addAssets');
+    }
+
+    public function addLocale(RegisterLocales $event)
+    {
+        $event->addTranslations('en', __DIR__.'/../../locale/en.yml');
+    }
+
+    public function addAssets(BuildClientView $event)
+    {
+        $event->forumAssets([
+            __DIR__.'/../../js/dist/extension.js',
+            __DIR__.'/../../less/extension.less'
+        ]);
+
+        $event->forumBootstrapper('{{name}}/main');
+
+        $event->forumTranslations([
+            // '{{name}}.hello_world'
+        ]);
+    }
+}

stubs/extension/src/ServiceProvider.php

@@ -1,39 +0,0 @@
-<?php namespace {{namespace}};
-
-use Flarum\Support\ServiceProvider;
-use Flarum\Extend;
-
-class {{classPrefix}}ServiceProvider extends ServiceProvider
-{
-    /**
-     * Bootstrap the application events.
-     *
-     * @return void
-     */
-    public function boot()
-    {
-        $this->extend([
-            (new Extend\Locale('en'))->translations(__DIR__.'/../locale/en.yml'),
-
-            (new Extend\ForumClient())
-                ->assets([
-                    __DIR__.'/../js/dist/extension.js',
-                    __DIR__.'/../less/extension.less'
-                ])
-                ->translations([
-                    // Add the keys of translations you would like to be available
-                    // for use by the JS client application.
-                ])
-        ]);
-    }
-
-    /**
-     * Register the service provider.
-     *
-     * @return void
-     */
-    public function register()
-    {
-        //
-    }
-}