Added hidden configuration option to enable/disable closing windows by clicking on menu button.

Option is called "CloseFromMenuButton"
It is false by default.
To turn it on, add
  CloseFromMenuButton=true
in [Windeco] section of $HOME/.kde4/share/config/oxygenrc.
Note that it results in poor usability of the menu button, if enabled.

CCBUG: 301237