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/private/notifmsg.h

@@ -0,0 +1,76 @@
+///////////////////////////////////////////////////////////////////////////////
+// Name:        wx/private/notifmsg.h
+// Purpose:     wxNotificationMessage declarations
+// Author:      Tobias Taschner
+// Created:     2015-08-04
+// Copyright:   (c) 2015 wxWidgets development team
+// Licence:     wxWindows licence
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef _WX_PRIVATE_NOTIFMSG_H_
+#define _WX_PRIVATE_NOTIFMSG_H_
+
+class wxNotificationMessageImpl
+{
+public:
+    wxNotificationMessageImpl(wxNotificationMessageBase* notification):
+        m_notification(notification),
+        m_active(false)
+    {
+
+    }
+
+    virtual ~wxNotificationMessageImpl() { }
+
+    virtual bool Show(int timeout) = 0;
+
+    virtual bool Close() = 0;
+
+    virtual void SetTitle(const wxString& title) = 0;
+
+    virtual void SetMessage(const wxString& message) = 0;
+
+    virtual void SetParent(wxWindow *parent) = 0;
+
+    virtual void SetFlags(int flags) = 0;
+
+    virtual void SetIcon(const wxIcon& icon) = 0;
+
+    virtual bool AddAction(wxWindowID actionid, const wxString &label) = 0;
+
+    virtual void Detach()
+    {
+        if (m_active)
+            m_notification = NULL;
+        else
+            delete this;
+    }
+
+    bool ProcessNotificationEvent(wxEvent& event)
+    {
+        if (m_notification)
+            return m_notification->ProcessEvent(event);
+        else
+            return false;
+    }
+
+    wxNotificationMessageBase* GetNotification() const
+    {
+        return m_notification;
+    }
+
+protected:
+    wxNotificationMessageBase* m_notification;
+    bool m_active;
+
+    void SetActive(bool active)
+    {
+        m_active = active;
+        
+        // Delete the implementation if the notification is detached
+        if (!m_notification && !active)
+            delete this;
+    }
+};
+
+#endif // _WX_PRIVATE_NOTIFMSG_H_