Deallocate menu buttons to save memory (#1971)

* Deallocate hidden menu buttons
* Added Copyright
* Added comments

firmware/application/ui/ui_btngrid.hpp

@@ -2,6 +2,7 @@
  * Copyright (C) 2014 Jared Boone, ShareBrained Technology, Inc.
  * Copyright (C) 2016 Furrtek
  * Copyright (C) 2019 Elia Yehuda (z4ziggy)
+ * Copyright (C) 2024 u-foka
  *
  * This file is part of PortaPack.
  *
@@ -73,10 +74,15 @@ class BtnGridView : public View {
     void set_arrow_enabled(bool enabled);
     void on_focus() override;
     void on_blur() override;
+    void on_show() override;
+    void on_hide() override;
     bool on_key(const KeyEvent event) override;
     bool on_encoder(const EncoderEvent event) override;
     bool blacklisted_app(GridItem new_item);
 
+   protected:
+    virtual void on_populate() = 0;
+
    private:
     int rows_{3};
     void update_items();