Added new EventExecutor, missed in last commit

By: stevenh <steven.hartland@multiplay.co.uk>

paper-api/src/main/java/org/bukkit/plugin/EventExecutor.java

@@ -0,0 +1,12 @@
+
+package org.bukkit.plugin;
+
+import org.bukkit.event.Event;
+import org.bukkit.event.Listener;
+
+/**
+ * Interface which defines the class for event call backs to plugins
+ */
+public interface EventExecutor {
+    public void execute( Listener listener, Event event );
+}