move all models into core

src/Core/Models/Api/Response/ResponseModel.cs

@@ -0,0 +1,19 @@
+using System;
+
+namespace Bit.Core.Models.Api
+{
+    public abstract class ResponseModel
+    {
+        public ResponseModel(string obj)
+        {
+            if(string.IsNullOrWhiteSpace(obj))
+            {
+                throw new ArgumentNullException(nameof(obj));
+            }
+
+            Object = obj;
+        }
+
+        public string Object { get; private set; }
+    }
+}