more methods to load plugins

Pilz.Plugins.Advanced/IPluginFeatureProvider.cs

@@ -0,0 +1,13 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Pilz.Plugins.Advanced
+{
+    public interface IPluginFeatureProvider<T> where T : PluginFeature
+    {
+        static abstract T Instance { get; }
+    }
+}