fix(ui): accordion_button leaks

Description

This fixes the memory leak caused by ui::qt::widget::accordion_menu::m_animation_group being allocated on the heap, but never freed.

How to test it?

• Launch ./bin/sight_viewer, click on accordion menus.
  • Exit while accordion menus are opened.
  • Exit while accordion menus are closed. None of the above should crash.
• Run valgrind (if you're really brave), and check no leaks occurs there.

Related issue(s)

Closes #1241 (closed)