Refactoring Refactoring icon, part 2

1. Add baidu, fix #576, #582
2. Refactoring

Plugins/Wox.Plugin.WebSearch/WebSearch.cs

@@ -1,12 +1,35 @@
-using System;
+using System.IO;
+using JetBrains.Annotations;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Serialization;
 
 namespace Wox.Plugin.WebSearch
 {
     public class WebSearch
     {
+        public const string DefaultIcon = "web_search.png";
         public string Title { get; set; }
         public string ActionKeyword { get; set; }
-        public string IconPath { get; set; }
+        [NotNull]
+        private string _icon = DefaultIcon;
+
+        [NotNull]
+        public string Icon
+        {
+            get { return _icon; }
+            set
+            {
+                _icon = value; 
+                IconPath = Path.Combine(WebSearchPlugin.PluginDirectory, WebSearchPlugin.ImageDirectory, value);
+            }
+        }
+        /// <summary>
+        /// All icon should be put under Images directory
+        /// </summary>
+        [NotNull]
+        [JsonIgnore]
+        internal string IconPath { get; private set; }
+
         public string Url { get; set; }
         public bool Enabled { get; set; }
     }