Revamp the structur of project database

sources/diagram.cpp

@@ -444,6 +444,14 @@ void Diagram::keyReleaseEvent(QKeyEvent *e)
 	}
 }
 
+/**
+ * @brief Diagram::uuid
+ * @return the uuid of this diagram
+ */
+QUuid Diagram::uuid() {
+	return m_uuid;
+}
+
 /**
  * @brief Diagram::setEventInterface
  * Set event_interface has current interface.