Add BypassGuestPassword configuration

Used to bypass the password for local connections

DearFTP/Configurations/ServerConfiguration.cs

@@ -13,5 +13,6 @@
         public string LogFilePath { get; set; } = "log.txt";
 
         public string Guest { get; set; } = "";
+        public bool BypassGuestPassword { get; set; } = false;
     }
 }

DearFTP/Connection/Commands/UserCommand.cs

@@ -1,4 +1,5 @@
 using DearFTP.Utils;
+using DearFTP.Utils.Extensions;
 using System;
 using System.Linq;
 
@@ -30,7 +31,7 @@ namespace DearFTP.Connection.Commands
 
                 user = configuration.Users.First(x => x.Name == guest);
             }
-            if (!string.IsNullOrWhiteSpace(user.Password))
+            if (!string.IsNullOrWhiteSpace(user.Password) && !(session.RemoteIP.IsInternal() && configuration.Server.BypassGuestPassword))
             {
                 stream.Send(ResponseCode.NeedPassword, "Please specify the password.");