Newline support in static text objects

[bluebear94]

I'm a bit surprised that GLUI_StaticText objects ignore newlines. Support for newlines inside static text would be helpful if you don't want to use multiple static text objects or the number of lines you need varies.

Edit: changes needed to support this:

• versions of GLUI_Control::draw_name, GLUI_Control::draw_string and _glutBitmapString that recognise newlines
• add methods GLUI_Control::string_dimensions and _glutBitmapDimensionsString that return both the width and height of text, recognising newlines
• modify the GLUI_StaticText class to use these methods