improve settings import/export

FluentTerminal.Models/MessageIdentifiers.cs

@@ -20,6 +20,7 @@
         GetCommandPathRequest = 15,
         PauseTerminalOutputRequest = 16,
         PauseTerminalOutputResponse = 17,
-        QuitApplicationRequest = 18
+        QuitApplicationRequest = 18,
+        ReadTextFileRequest = 19
     }
 }