Fix potential compile error

This compiled just fine for me but apparently the QStringList needs to be
explicitly included on Ubuntu 15.10.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

subsurface-core/subsurface-qt/DiveObjectHelper.h

@@ -4,6 +4,7 @@
 #include "../dive.h"
 #include <QObject>
 #include <QString>
+#include <QStringList>
 
 class DiveObjectHelper : public QObject {
     Q_OBJECT
@@ -89,4 +90,4 @@ private:
 };
 Q_DECLARE_METATYPE(DiveObjectHelper*)
 
-#endif
+#endif