images: cache default photo

It takes up to 40% of memory when app is loading
This image is now cached in a QHash with a key computed from the size
asked.

Change-Id: Iebb14e9c38dbd6e9057c9fbe5a366542fefffca5
Tuleap: #663
diff --git a/src/delegates/ImageManipulationDelegate.h b/src/delegates/ImageManipulationDelegate.h
index 43e7446..9605ba3 100644
--- a/src/delegates/ImageManipulationDelegate.h
+++ b/src/delegates/ImageManipulationDelegate.h
@@ -21,13 +21,14 @@
 
 //Qt
 #import <QSize>
+#import <QtGui/qpixmap.h>
 
 //Ring
 #import <interfaces/pixmapmanipulatori.h>
 #import <call.h>
 
 class Person;
-class QPixmap;
+class QString;
 
 namespace Interfaces {
 
@@ -61,6 +62,8 @@
         QPixmap drawDefaultUserPixmap(const QSize& size, bool displayPresence = false, bool isPresent = false);
         CGImageRef resizeCGImage(CGImageRef image, const QSize& size);
 
+        QHash<QString, QPixmap> m_hDefaultUserPixmap;
+
         /**
          * Return a version of size destSize centered of the bigger photo
          */