Add missing include statements.

src/core/Database.h

@@ -20,6 +20,7 @@
 
 #include <QDateTime>
 #include <QHash>
+#include <QObject>
 
 #include "core/Uuid.h"
 #include "keys/CompositeKey.h"

src/gui/group/GroupView.cpp

@@ -19,6 +19,7 @@
 
 #include <QDragMoveEvent>
 #include <QMetaObject>
+#include <QMimeData>
 
 #include "core/Database.h"
 #include "core/Group.h"

tests/gui/TestGui.cpp

@@ -21,6 +21,7 @@
 #include <QApplication>
 #include <QDialogButtonBox>
 #include <QLineEdit>
+#include <QMimeData>
 #include <QPushButton>
 #include <QSpinBox>
 #include <QTemporaryFile>