Restructure wxNotificationMessage.

wxNotificationMessage has been refactored to always use wxNotificationMessageImpl (this was previously already done in the MSW implementation)

This adds various features and fixes to wxNotificationMessage:
- OS X Notification Center implementation
- Generic "toast" notifications
- SetIcon() to specify a custom icon
- AddAction() to add actions to notifications
- Events to get notify of notification clicks, dismiss or actions

include/wx/generic/private/notifmsg.h

@@ -0,0 +1,52 @@
+///////////////////////////////////////////////////////////////////////////////
+// Name:        wx/generic/private/notifmsg.h
+// Purpose:     wxGenericNotificationMessage declarations
+// Author:      Tobias Taschner
+// Created:     2015-08-04
+// Copyright:   (c) 2015 wxWidgets development team
+// Licence:     wxWindows licence
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef _WX_GENERIC_PRIVATE_NOTIFMSG_H_
+#define _WX_GENERIC_PRIVATE_NOTIFMSG_H_
+
+#include "wx/private/notifmsg.h"
+
+class wxGenericNotificationMessageImpl : public wxNotificationMessageImpl
+{
+public:
+    wxGenericNotificationMessageImpl(wxNotificationMessageBase* notification);
+
+    virtual ~wxGenericNotificationMessageImpl();
+
+    virtual bool Show(int timeout) wxOVERRIDE;
+
+    virtual bool Close() wxOVERRIDE;
+
+    virtual void SetTitle(const wxString& title) wxOVERRIDE;
+
+    virtual void SetMessage(const wxString& message) wxOVERRIDE;
+
+    virtual void SetParent(wxWindow *parent) wxOVERRIDE;
+
+    virtual void SetFlags(int flags) wxOVERRIDE;
+
+    virtual void SetIcon(const wxIcon& icon) wxOVERRIDE;
+
+    virtual bool AddAction(wxWindowID actionid, const wxString &label) wxOVERRIDE;
+
+    // get/set the default timeout (used if Timeout_Auto is specified)
+    static int GetDefaultTimeout() { return ms_timeout; }
+    static void SetDefaultTimeout(int timeout);
+
+private:
+    // default timeout
+    static int ms_timeout;
+
+    // notification message is represented by a frame in this implementation
+    class wxNotificationMessageWindow *m_window;
+
+    wxDECLARE_NO_COPY_CLASS(wxGenericNotificationMessageImpl);
+};
+
+#endif // _WX_GENERIC_PRIVATE_NOTIFMSG_H_