Web search suggestion is loaded async

1. suggestion is async
2. if ping time of domain less than 300ms, then suggestion is still sync
3. #578 #539

Wox.Plugin/Result.cs

@@ -7,6 +7,7 @@ namespace Wox.Plugin
 
     public class Result
     {
+
         private string _pluginDirectory;
         private string _icoPath;
         public string Title { get; set; }