🎉 Make it possible to select window open effects

prefs.js

@@ -138,6 +138,28 @@ var PreferencesDialog = class PreferencesDialog {
         // clang-format on
       }
 
+      // Populate the open-effects drop-down menu.
+      {
+        const menu  = this._builder.get_object('open-effect-menu');
+        const group = Gio.SimpleActionGroup.new();
+        window.insert_action_group('open-effects', group);
+
+        ALL_EFFECTS.forEach(Effect => {
+          const [minMajor, minMinor] = Effect.getMinShellVersion();
+          if (utils.shellVersionIsAtLeast(minMajor, minMinor)) {
+            const nick       = Effect.getNick();
+            const label      = Effect.getLabel();
+            const actionName = nick + '-open-effect';
+            const fullName   = 'open-effects.' + actionName;
+
+            const action = this._settings.create_action(actionName);
+            group.add_action(action);
+
+            menu.append_item(Gio.MenuItem.new(label, fullName));
+          }
+        });
+      }
+
       // Populate the close-effects drop-down menu.
       {
         const menu  = this._builder.get_object('close-effect-menu');
@@ -299,8 +321,12 @@ var PreferencesDialog = class PreferencesDialog {
           this._button.connect('clicked', () => {
 
             // Set the to-be-previewed effect.
+            dialog.getSettings().set_string('open-preview-effect', Effect.getNick());
             dialog.getSettings().set_string('close-preview-effect', Effect.getNick());
 
+            // Make sure that the window.show() firther below "sees" this change.
+            Gio.Settings.sync();
+
             // Create the preview-window.
             const window = new Gtk.Window({
               title: `Preview for ${Effect.getLabel()}`,