handling offline and inassisable db in oe (#369)

* handling offline and inassisable db in oe

src/Microsoft.SqlTools.ServiceLayer/ObjectExplorer/Nodes/ChildFactory.cs

@@ -37,6 +37,11 @@ namespace Microsoft.SqlTools.ServiceLayer.ObjectExplorer.Nodes
         /// </summary>
         public abstract IEnumerable<NodeFilter> Filters { get; }
 
+        /// <summary>
+        /// The list of properties to be loaded with the object
+        /// </summary>
+        public abstract IEnumerable<NodeSmoProperty> SmoProperties { get; }
+
         /// <summary>
         /// Returns the node sub type if the object can have sub types otehr wise returns empty string
         /// </summary>