Add functionality to ensure that the basic system works

There are some things missing:

- Configuration
- Resuming downloads when the list doesn't scroll past the window

src/mainwindow.h

@@ -24,6 +24,9 @@
 #define DANBOORU_CLIENT_H
 
 #include <kxmlguiwindow.h>
+#include <KSharedDataCache>
+#include <KImageCache>
+
 
 class QQuickWidget;
 
@@ -71,6 +74,7 @@ private:
     DanbooruPostModel *m_model;
     DanbooruService *m_service;
     DanbooruConnectWidget *m_connectWidget;
+    KImageCache *m_cache;
 
 };
 } // namespace Danbooru