Release v0.6 bug bp copy (#1341)

* Fix fro BrainParameter copy between brains

* Removed useless imports

UnitySDK/Assets/ML-Agents/Editor/BrainEditor.cs

-using System.Collections;
-using System.Collections.Generic;
-using UnityEngine;
+using UnityEngine;
+using UnityEditor;
-using UnityEditor;
-using System.Linq;
 
 namespace MLAgents
 {
             if (brainToCopy != null)
             {
                 brain.brainParameters = brainToCopy.brainParameters.Clone();
+                EditorUtility.SetDirty(brain);
+                AssetDatabase.SaveAssets();
+                return;
             }
             var serializedBrain = serializedObject;
             serializedBrain.Update(); 
             EditorGUILayout.LabelField("", GUI.skin.horizontalSlider);
         }
     }
-}
+}