Databinding for hotkey tab

part of #660

Wox.Core/UserSettings/PluginSettings.cs

@@ -1,10 +1,12 @@
 using System.Collections.Generic;
 using System.Linq;
+using PropertyChanged;
 using Wox.Core.Plugin;
 using Wox.Plugin;
 
 namespace Wox.Core.UserSettings
 {
+    [ImplementPropertyChanged]
     public class PluginsSettings
     {
         public string PythonDirectory { get; set; }