Added commandbuilder.then() and argumentbuilder

src/main/java/net/minecraft/commands/builder/ArgumentBuilder.java

@@ -0,0 +1,18 @@
+package net.minecraft.commands.builder;
+
+import com.google.common.collect.Lists;
+
+import java.util.List;
+
+public abstract class ArgumentBuilder {
+    private final List<ArgumentBuilder> arguments = Lists.newArrayList();
+
+    public ArgumentBuilder then(ArgumentBuilder argument) {
+        arguments.add(argument);
+        return this;
+    }
+
+    public List<ArgumentBuilder> getArguments() {
+        return arguments;
+    }
+}