Creates data integrity health checks

src/Umbraco.Core/Services/IContentServiceBase.cs

@@ -5,5 +5,16 @@
     /// TODO: Start sharing the logic!
     /// </summary>
     public interface IContentServiceBase : IService
-    { }
+    {
+
+        /// <summary>
+        /// Checks the data integrity of the node paths/levels stored in the database
+        /// </summary>
+        bool VerifyNodePaths(out int[] invalidIds);
+
+        /// <summary>
+        /// Fixes the data integrity of node paths/levels stored in the database
+        /// </summary>
+        void FixNodePaths();
+    }
 }