Move wxAdv library contents into wxCore

This basically removes the "adv" library, even though it's still
preserved for compatibility with user make/project files referring to
it.

It is done because the distinction between "adv" and "core" was never
really clear (e.g. why wxTreeCtrl was in core but wxTreeListCtrl in
adv?) and it prevented some core classes from using adv ones.

include/wx/xrc/xmlreshandler.h

@@ -21,7 +21,7 @@
 #include "wx/imaglist.h"
 #include "wx/window.h"
 
-class WXDLLIMPEXP_FWD_ADV wxAnimation;
+class WXDLLIMPEXP_FWD_CORE wxAnimation;
 
 class WXDLLIMPEXP_FWD_XML wxXmlNode;
 class WXDLLIMPEXP_FWD_XML wxXmlResource;