Made every CommandNode support an executor

src/main/java/net/minecraft/commands/tree/CommandNode.java

@@ -7,8 +7,17 @@ import net.minecraft.commands.exceptions.IllegalArgumentSyntaxException;
 import java.util.List;
 
 public abstract class CommandNode {
+    private final Runnable executor;
     private final List<CommandNode> children = Lists.newArrayList();
 
+    protected CommandNode(Runnable executor) {
+        this.executor = executor;
+    }
+
+    public Runnable getExecutor() {
+        return executor;
+    }
+
     public List<CommandNode> getChildren() {
         return children;
     }