implement work_path for documents and data_path for assets

src/node_canvas.cpp

@@ -53,7 +53,7 @@ void NodeCanvas::restore_context()
 void NodeCanvas::clear_context()
 {
     Node::clear_context();
-    m_canvas->snapshot_save(data_path);
+    m_canvas->snapshot_save();
     m_canvas->clear_context();
     // TODO: clear CanvasMode objects
 }