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/JoystickButton.h

@@ -0,0 +1,30 @@
+/*----------------------------------------------------------------------------*/
+/* 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/GenericHID.h"
+#include "frc/buttons/Button.h"
+
+namespace frc {
+
+class JoystickButton : public Button {
+ public:
+  JoystickButton(GenericHID* joystick, int buttonNumber);
+  virtual ~JoystickButton() = default;
+
+  JoystickButton(JoystickButton&&) = default;
+  JoystickButton& operator=(JoystickButton&&) = default;
+
+  virtual bool Get();
+
+ private:
+  GenericHID* m_joystick;
+  int m_buttonNumber;
+};
+
+}  // namespace frc