LCD Progress Bar

Display a graphical progress bar on the bottom line of the LCD during SD printing if there's no other LCD message. To gain this feature we sacrifice three other custom characters, substituting \xDF for the "degree" character, a blank space for the "clock" character, and caret (^) for the "uplevel" character. Rumor has it you can substitute custom characters on the fly, so it may be possible to get this feature without sacrificing other custom characters, but this hasn't been tried yet.