Feature request: UI: Improve visibility of selected items in system tray menu

[ags1234]

The selected option in the system tray menu is hard to see as it is now, a trans-lucid, barely visible rectangle.
Exemplified in the attached picture.

Clear visibility is important in an UI. For the user it is not all the same if all traffic is blocked or all traffic is allowed.
The selected options should be clearly marked.

[tnodir]

It depends on Qt's styling.

The "Filter Mode" menu item has same icon as selected mode.