Some applications have the functionality of minimizing to "icon tray" directly. Others don't.
We present: ALLTRAY
$ sudo apt-get install alltray
to configure programs to minimize to icon tray, just add «alltray» before the text presented in command:
(right click » Properties - to show this windows)
to minimize to icon tray just double click on the icon in icon tray;
to minimize as usual just click on the minimize button in the respective window.