Expose more properties of the connection validator context in MQTTnet.Server. Migrate return code to reason code.

Source/MQTTnet.Server/Configuration/ScriptingSettingsModel.cs

@@ -4,6 +4,8 @@ namespace MQTTnet.Server.Configuration
 {
     public class ScriptingSettingsModel
     {
+        public string ScriptsPath { get; set; }
+
         public List<string> IncludePaths { get; set; }
     }
 }