Use same key for exiting a mode as for entering it

Thos makes it easier to quickly abort the mode if entered by accident.

dotfiles/i3/config

   bindsym u     exec i3-winmark unmark ; mode "default"
   bindsym g     exec i3-winmark goto   ; mode "default"
 
+  bindsym $mod+equal mode "default"
   bindsym Escape mode "default"
   bindsym Return mode "default"
 }
         bindsym Shift+Down  resize grow     height  25 px or 2 ppt
         bindsym Shift+Up    resize shrink   height  25 px or 2 ppt
         bindsym Shift+Right resize grow     width   25 px or 2 ppt
+        bindsym $mod+r      mode "default"
         bindsym Return      mode "default"
         bindsym Escape      mode "default"
 }