Enable colour codes for drawing text.

- Added colour code functionality to the GLUI classes.
  - Use the escape sequence \c#RRGGBB in text to set the text colour, for
    example:

	"\c#FFFFFFThis is some white text. \c#FF0000This is red text."

  - You can use colour codes inside words:

    	"\c#FF0000R\c#FF9900a\c#FFFF00i\c#00FF00n\c#0000FFb\c#FF00FFo"+
	"\c#6633CCw\c#FFFFFF!"
Resize blank.png to 16x16.