overhaul provider structure

OwnChar.Server/Commands/IServerCommand.cs

@@ -0,0 +1,15 @@
+using Pilz.Plugins.Advanced;
+
+namespace OwnChar.Server.Commands
+{
+    public interface IServerCommand
+    {
+        // Shared
+        public const string FeatureCode = "ownchar.server.command";
+        public IEnumerable<IServerCommand> Commands => PluginFeatureController.Instance.Features.Get(FeatureCode).Cast<PluginFunction>().Select(f => (IServerCommand)f.Execute()!);
+
+        // Interface
+        public string Command { get; }
+        public string Description { get; }
+    }
+}