Adds RequiredForPersistenceAttribute to easily detect if any entity fails validation in a way that it cannot be persisted to the data store. Changes all tree events to not be jquery events and to not require a 'callback' jquery object, instead we just use angular events broadcast globally, much nicer.

src/Umbraco.Core/Models/Validation/RequiredForPersistenceAttribute.cs

@@ -0,0 +1,23 @@
+using System;
+using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Web.ModelBinding;
+
+namespace Umbraco.Core.Models.Validation
+{
+    /// <summary>
+    /// A custom validation attribute which adds additional metadata to the property to indicate that 
+    /// the value is required to be persisted.
+    /// </summary>
+    /// <remarks>
+    /// In Umbraco, we persist content even if it is invalid, however there are some properties that are absolutely required
+    /// in order to be persisted such as the Name of the content item. This attribute is re-usable to check for these types of
+    /// properties over any sort of model.
+    /// </remarks>
+    public class RequiredForPersistenceAttribute : RequiredAttribute
+    {
+    }
+}