Implement new ListView interface requirements

Author: StayTalm

Runtime/Scripts/Data/AssetData.cs

@@ -20,6 +20,8 @@ sealed class AssetData : IListViewItemData<int>
         public string type { get; private set; }
         public GameObject preview { get; set; }
 
+        public bool selected => false;
+
         public Object asset
         {
             get { return m_Asset; }

Runtime/Workspaces/PolyWorkspace/Scripts/PolyGridAsset.cs

@@ -34,6 +34,7 @@ class PolyGridAsset : IListViewItemData<string>, IUsesWeb
         public string template { get { return k_TemplateName; } }
 
         public string index { get; private set; }
+        public bool selected => false;
         public PolyAsset asset { get { return m_Asset; } }
         public GameObject prefab { get { return m_Prefab; } }
         public Texture2D thumbnail { get { return m_Thumbnail; } }