Add threaded processing of image pixmaps

This code adds threaded processing of a batch of images. It uses the
QtConcurrent implementations to call a function repeteadly using
MAX_THREADS (Qt gets that for us) and returns a list of it.

This call is blocking, so while the pixmaps are being scaled in threads,
it will wait for all scalling to be done.

Signed-off-by: Tomaz Canabrava <tomaz.canabrava@intel.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

qt-ui/divepicturewidget.h

@@ -16,6 +16,10 @@ public:
 	void updateDivePictures(int divenr);
 private:
 	int numberOfPictures;
+	// Currently, load the images on the fly
+	// Later, use a thread to load the images
+	// Later, save the thumbnails so we don't need to reopen every time.
+	QHash<QString, QPixmap> stringPixmapCache;
 };
 
 class DivePictureDelegate : QStyledItemDelegate {