Implement scrolling for text chat.
If text chat box is active, then allow chat history to be scrolled (up to n lines) via mouse scrollwheel, PgUp/PgDn, and mouse-draggable scrollbar.
If text chat box is active, then allow chat history to be scrolled (up to n lines) via mouse scrollwheel, PgUp/PgDn, and mouse-draggable scrollbar.