HaikuDepot: Added TODO.
HaikuDepot: Make MarkupParser a bit more flexible...

 ... by allowing to append markup to an existing document.
HaikuDepot: Added TextView::ParagraphStyle() ...

 ... to get the initial/default paragraph style.
HaikuDepot: Use TextDocumentView for package description.

 * The rating items are also justified for consistency.
 * Refactored usages of TextDocumentView and MarkupParser into
   MarkupTextView.
HaikuDepot: TextDocument-Layout and -View optimize drawing...

 ... by drawing only the paragraphs that intersect with the
 update rect.
HaikuDepot: Introduced LinkView utility class

 * Inherits BStringView
 * Highlights string on hover and changes cursor shape.
 * Sends message when clicked.