Fixed missing namespace prefix on properties that is set as elements on types outside default XAML namespace.

Fixing this in CreatePropertyElement method also fixed another bug for AddChildNodeToProperty method that was fixed earlier in InsertNodeInCollection method with commit comment as follows:
"Its WPF standard to use parent type name as prefix before the dot when declaring a property as XAML element, and NOT the name of the type that declares the property."

src/AddIns/DisplayBindings/WpfDesign/WpfDesign.XamlDom/Project/XamlProperty.cs

@@ -268,6 +268,16 @@ namespace ICSharpCode.WpfDesign.XamlDom
 			}
 		}
 
+        XmlElement CreatePropertyElement()
+        {
+            string ns = parentObject.OwnerDocument.GetNamespaceFor(parentObject.ElementType);
+            return parentObject.OwnerDocument.XmlDocument.CreateElement(
+                parentObject.OwnerDocument.GetPrefixForNamespace(ns),
+                parentObject.ElementType.Name + "." + this.PropertyName,
+                ns
+                );
+        }
+		
 		internal void AddChildNodeToProperty(XmlNode newChildNode)
 		{
 			if (this.IsCollection) {
@@ -280,10 +290,7 @@ namespace ICSharpCode.WpfDesign.XamlDom
 					parentObject.XmlElement.InsertBefore(newChildNode, parentObject.XmlElement.FirstChild);
 					return;
 				}
-				_propertyElement = parentObject.OwnerDocument.XmlDocument.CreateElement(
+                _propertyElement = CreatePropertyElement();
-					this.PropertyTargetType.Name + "." + this.PropertyName,
-					parentObject.OwnerDocument.GetNamespaceFor(this.PropertyTargetType)
-				);
 				parentObject.XmlElement.InsertBefore(_propertyElement, parentObject.XmlElement.FirstChild);
 			}
 			_propertyElement.AppendChild(newChildNode);
@@ -296,10 +303,7 @@ namespace ICSharpCode.WpfDesign.XamlDom
 			if (collection == null) {
 				if (collectionElements.Count == 0 && this.PropertyName != this.ParentObject.ContentPropertyName) {
 					// we have to create the collection element
-					_propertyElement = parentObject.OwnerDocument.XmlDocument.CreateElement(
+                    _propertyElement = CreatePropertyElement();
-						ParentObject.ElementType.Name + "." + this.PropertyName,
-						parentObject.OwnerDocument.GetNamespaceFor(ParentObject.ElementType)
-					);
 
 					if (this.IsResources) {
 						parentObject.XmlElement.PrependChild(_propertyElement);