Refactor the web app bootstrapping code

- All custom JS variables are now preloaded into the `app.data` object, rather than directly on the `app` object. This means that admin settings are available in `app.data.settings` rather than `app.settings`, etc.
- Cleaner route handler generation
- Renamed ConfigureClientView to ConfigureWebApp, though the former still exists and is deprecated
- Partial fix for #881 (strips ?nojs=1 from URL if possible, so that refreshing will attempt to load JS version again)

stubs/extension/src/Listener/AddClientAssets.php

@@ -1,16 +1,16 @@
 <?php namespace {{namespace}}\Listener;
 
-use Flarum\Event\ConfigureClientView;
+use Flarum\Event\ConfigureWebApp;
 use Illuminate\Contracts\Events\Dispatcher;
 
 class AddClientAssets
 {
     public function subscribe(Dispatcher $events)
     {
-        $events->listen(ConfigureClientView::class, [$this, 'addAssets']);
+        $events->listen(ConfigureWebApp::class, [$this, 'addAssets']);
     }
 
-    public function addAssets(ConfigureClientView $event)
+    public function addAssets(ConfigureWebApp $event)
     {
         if ($event->isForum()) {
             $event->addAssets([