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)

js/admin/src/utils/saveSettings.js

@@ -1,14 +1,14 @@
 export default function saveSettings(settings) {
-  const oldSettings = JSON.parse(JSON.stringify(app.settings));
+  const oldSettings = JSON.parse(JSON.stringify(app.data.settings));
 
-  Object.assign(app.settings, settings);
+  Object.assign(app.data.settings, settings);
 
   return app.request({
     method: 'POST',
     url: app.forum.attribute('apiUrl') + '/settings',
     data: settings
   }).catch(error => {
-    app.settings = oldSettings;
+    app.data.settings = oldSettings;
     throw error;
   });
 }