Move revealers access away from base classes

Those should not appear in base classes, as they are available in main app only

src/app.js

@@ -1,4 +1,4 @@
-const { Gio, GObject, Gtk } = imports.gi;
+const { Gio, GObject, Gdk, Gtk } = imports.gi;
 const { AppBase } = imports.src.appBase;
 const { Widget } = imports.src.widget;
 const Debug = imports.src.debug;
@@ -43,6 +43,22 @@ class ClapperApp extends AppBase
         this._openFilesAsync(files).then(() => this.activate()).catch(debug);
     }
 
+    _onIconThemeChanged(gtkSettings)
+    {
+        super._onIconThemeChanged(gtkSettings);
+
+        const display = Gdk.Display.get_default();
+        if(!display) return;
+
+        const iconTheme = Gtk.IconTheme.get_for_display(display);
+        if(!iconTheme) return;
+
+        const { headerBar } = this.active_window.child.revealerTop;
+        if(!headerBar) return;
+
+        headerBar._onIconThemeChanged(iconTheme);
+    }
+
     _onWindowMap(window)
     {
         window.disconnect(this.mapSignal);