Add support for WPF controls in plugins and method parameters in plugin commands

Torch.API/Plugins/IWpfPlugin.cs

@@ -0,0 +1,18 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Windows.Controls;
+
+namespace Torch.API.Plugins
+{
+    public interface IWpfPlugin : ITorchPlugin
+    {
+        /// <summary>
+        /// Used by the server's WPF interface to load custom plugin controls.
+        /// Do not instantiate your plugin control outside of this method! It will throw an exception.
+        /// </summary>
+        UserControl GetControl();
+    }
+}