Re-Introduce Thunar Tray Icon for Transfer Dialog via StatusNotifier API

Hello. In 4.16 i did huge copy/move opperations from thunar and when i close process information window it minimized to tray and i can control and see proces if i need.

In 4.18 after close copy/move opperations information window it disapear (NOT minimized to tray), but data transferring and process work!

Probably bug !