[Server] Allow multiple sessions with one user

ServerLib/ICWebservice.cs

@@ -71,6 +71,11 @@ namespace ServerLib
             UriTemplate = "/login?username={username}&password={password}")]
         Guid Login(string username, string password);
 
+        [OperationContract, WebInvoke(Method = "GET",
+            ResponseFormat = WebMessageFormat.Json,
+            UriTemplate = "/logout")]
+        void Logout();
+
         [OperationContract, WebInvoke(Method = "GET",
             ResponseFormat = WebMessageFormat.Json,
             UriTemplate = "")]