feature request: Add setting that removes program from the tray and finishes the process when user clicks "Close" button

[SpamBot-zz]

Description

When user need is to run an onetime on demand scan without schedules, it looks more natural to actually close the window instead of hiding it and keeping the process running in the background when user clicks "Close" button.
Currently, user have to finish the process through the tray icon's context menu.

Proposed solution

Add corresponding setting to the "Settings" dialog.