DDMsgReader: Scrolling ANSI and "use strict" improvements

Graphic is now only used when using the scrollable interface. Also, when creating the Graphic, now subtracting 1 from the reading area height to avoid making the Graphic one line too tall to avoid unnecessary scrolling.
When saving messages with ANSI codes, Graphic is only used if the message has any ASCII drawing characters. (not sure if this really matters much though).
Also, applied "use strict" and made some changes as necessary.