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/gtk/notifmsg.h

@@ -1,51 +0,0 @@
-///////////////////////////////////////////////////////////////////////////////
-// Name:        wx/gtk/notifmsg.h
-// Purpose:     wxNotificationMessage for wxGTK.
-// Author:      Vadim Zeitlin
-// Created:     2012-07-25
-// Copyright:   (c) 2012 Vadim Zeitlin <vadim@wxwidgets.org>
-// Licence:     wxWindows licence
-///////////////////////////////////////////////////////////////////////////////
-
-#ifndef _WX_GTK_NOTIFMSG_H_
-#define _WX_GTK_NOTIFMSG_H_
-
-typedef struct _NotifyNotification NotifyNotification;
-
-// ----------------------------------------------------------------------------
-// wxNotificationMessage
-// ----------------------------------------------------------------------------
-
-class WXDLLIMPEXP_ADV wxNotificationMessage : public wxNotificationMessageBase
-{
-public:
-    wxNotificationMessage() { Init(); }
-    wxNotificationMessage(const wxString& title,
-                          const wxString& message = wxString(),
-                          wxWindow *parent = NULL,
-                          int flags = wxICON_INFORMATION)
-        : wxNotificationMessageBase(title, message, parent, flags)
-    {
-        Init();
-    }
-
-    virtual ~wxNotificationMessage();
-
-
-    virtual bool Show(int timeout = Timeout_Auto) wxOVERRIDE;
-    virtual bool Close() wxOVERRIDE;
-
-    // Set the name of the icon to use, overriding the default icon determined
-    // by the flags. Call with empty string to reset custom icon.
-    bool GTKSetIconName(const wxString& name);
-
-private:
-    void Init() { m_notification = NULL; }
-
-    NotifyNotification* m_notification;
-    wxString m_iconName;
-
-    wxDECLARE_NO_COPY_CLASS(wxNotificationMessage);
-};
-
-#endif // _WX_GTK_NOTIFMSG_H_