序列化bug修复，近期主要修复bug为主

AIStudio.Wpf.DiagramDesigner/Models/Serializables/DesignerItemBase.cs

@@ -107,18 +107,45 @@ namespace AIStudio.Wpf.DiagramDesigner
             get; set;
         }
 
-        [XmlAttribute]
+        [XmlIgnore]
         public CornerRadius CornerRadius
         {
             get; set;
         }
 
-        [XmlAttribute]
+        [JsonIgnore]
+        [XmlElement("CornerRadius")]
+        public string XmlCornerRadius
+        {
+            get
+            {
+                return SerializeHelper.SerializeCornerRadius(CornerRadius);
+            }
+            set
+            {
+                CornerRadius = SerializeHelper.DeserializeCornerRadius(value);
+            }
+        }
+
+        [XmlIgnore]
         public Thickness BorderThickness
         {
             get; set;
         }
 
+        [JsonIgnore]
+        [XmlElement("BorderThickness")]
+        public string XmlBorderThickness
+        {
+            get
+            {
+                return SerializeHelper.SerializeThickness(BorderThickness);
+            }
+            set
+            {
+                BorderThickness = SerializeHelper.DeserializeThickness(value);
+            }
+        }
 
         [XmlArray]
         public List<FullyCreatedConnectorInfoItem> Connectors