Enable X window notification on bell character

dotfiles/config/xfce4/terminal/terminalrc

 BackgroundMode=TERMINAL_BACKGROUND_IMAGE
 BackgroundDarkness=0.950000
 TitleMode=TERMINAL_TITLE_REPLACE
-MiscBellUrgent=FALSE
+MiscBellUrgent=TRUE
 MiscMouseWheelZoom=TRUE
 MiscMiddleClickOpensUri=FALSE
 MiscCopyOnSelect=FALSE