New: Add PID to Resource

(coscine/issues#469)

src/Project/ReturnObjects/ResourceObject.cs

@@ -9,6 +9,7 @@ namespace Coscine.Api.Project.ReturnObjects
     public class ResourceObject : IReturnObject
     {
         public Guid Id { get; set; }
+        public string PID { get { return Program.Configuration.GetStringAndWait("coscine/global/epic/prefix") + "/" + Id.ToString(); } }
         public string DisplayName { get; set; }
         public string ResourceName { get; set; }
         public string Description { get; set; }