public and private keys added to db and user domain. added account APIs got getting and putting keys.

src/Api/Models/Response/KeysResponseModel.cs

@@ -0,0 +1,23 @@
+using System;
+using Bit.Core.Domains;
+
+namespace Bit.Api.Models
+{
+    public class KeysResponseModel : ResponseModel
+    {
+        public KeysResponseModel(User user)
+            : base("keys")
+        {
+            if(user == null)
+            {
+                throw new ArgumentNullException(nameof(user));
+            }
+
+            PublicKey = user.PublicKey;
+            PrivateKey = user.PrivateKey;
+        }
+
+        public string PublicKey { get; set; }
+        public string PrivateKey { get; set; }
+    }
+}