implement Session-API, fix code selection problem for the Demo Web-App.

ElectronNET.API/WebContents.cs

@@ -20,6 +20,11 @@ namespace ElectronNET.API
         /// </value>
         public int Id { get; private set; }
 
+        /// <summary>
+        /// Manage browser sessions, cookies, cache, proxy settings, etc.
+        /// </summary>
+        public Session Session { get; internal set; }
+
         /// <summary>
         /// Emitted when the renderer process crashes or is killed.
         /// </summary>
@@ -82,6 +87,7 @@ namespace ElectronNET.API
         internal WebContents(int id)
         {
             Id = id;
+            Session = new Session(id);
         }
 
         /// <summary>