LCD Progress Bar

Display a graphical progress bar on the bottom line of the LCD during SD printing if there's no other LCD status message. If there is a message, display it in alternation with the progress bar, about every 2 seconds with a normal lcd update rate. (Alternatively, messages can appear once for a period of time and then hide.)

This feature makes it easier to gauge print progress from across the room, or at a glance.

To draw the graphical progress bar we needed to borrow three custom characters that don't appear on the Info Screen. There was no way to re-initialize the custom characters in response to a menu change, so hooks have been added to the ultralcd and hitachi lcd code. (New custom characters may be added to enhance other sub-menus by modifying this hook.)