Split the two command implementations into separate libraries (#2012)

This will allow us at the user code side to determine to include old commands, new commands or both.

wpilibOldCommands/src/main/native/include/frc/buttons/CancelButtonScheduler.h

@@ -0,0 +1,28 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2011-2019 FIRST. All Rights Reserved.                        */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include "frc/buttons/ButtonScheduler.h"
+
+namespace frc {
+
+class Trigger;
+class Command;
+
+class CancelButtonScheduler : public ButtonScheduler {
+ public:
+  CancelButtonScheduler(bool last, Trigger* button, Command* orders);
+  virtual ~CancelButtonScheduler() = default;
+
+  CancelButtonScheduler(CancelButtonScheduler&&) = default;
+  CancelButtonScheduler& operator=(CancelButtonScheduler&&) = default;
+
+  virtual void Execute();
+};
+
+}  // namespace frc