add string representation of state

include/cell.h

@@ -15,6 +15,19 @@ struct Cell
     WORKING
   };
 
+  std::string stateString() const {
+    switch (state) {
+      case DISCONNECTED:
+        return "DISCONNECTED";
+      case IDLE:
+        return "IDLE";
+      case WORKING:
+        return "WORKING";
+      default:
+        return "UNDEFINED";
+    }
+  }
+
   std::string id;
   Scene scene;
   State state = UNDEFINED;