♻️ Refactor how preferences pages are set up

src/Wisps.js

@@ -58,7 +58,7 @@ var Wisps = class Wisps {
   // This is called by the preferences dialog. It loads the settings page for this effect,
   // binds all properties to the settings and appends the page to the main stack of the
   // preferences dialog.
-  static initPreferences(dialog) {
+  static getPreferences(dialog) {
 
     // Add the settings page to the builder.
     dialog.getBuilder().add_from_resource(`/ui/${utils.getGTKString()}/Wisps.ui`);
@@ -68,10 +68,8 @@ var Wisps = class Wisps {
     dialog.bindAdjustment('wisps-scale');
     dialog.bindColorButton('wisps-color');
 
-    // Finally, append the settings page to the main stack.
-    const stack = dialog.getBuilder().get_object('main-stack');
-    stack.add_titled(
-        dialog.getBuilder().get_object('wisps-prefs'), Wisps.getNick(), Wisps.getLabel());
+    // Finally, return the new settings page.
+    return dialog.getBuilder().get_object('wisps-prefs');
   }
 
   // ---------------------------------------------------------------- API for extension.js