Add togglemenu command

Allow togglemenu to be run in binds while in menu or message mode.

README

@@ -281,6 +281,8 @@ New commands
   stopvideo               - stop video capture
   stopmusic               - stop background music
   minimize                - Minimize the game and show desktop
+  togglemenu              - causes escape key event for opening/closing menu, or
+                            going to a pervious menu. works in binds, even in UI
 
   print                   - print out the contents of a cvar
   unset                   - unset a user created cvar