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/msw/taskbar.h

@@ -15,9 +15,9 @@
 #include "wx/icon.h"
 
 // private helper class:
-class WXDLLIMPEXP_FWD_ADV wxTaskBarIconWindow;
+class WXDLLIMPEXP_FWD_CORE wxTaskBarIconWindow;
 
-class WXDLLIMPEXP_ADV wxTaskBarIcon : public wxTaskBarIconBase
+class WXDLLIMPEXP_CORE wxTaskBarIcon : public wxTaskBarIconBase
 {
 public:
     wxTaskBarIcon(wxTaskBarIconType iconType = wxTBI_DEFAULT_TYPE);