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/cpp/buttons/Button.cpp

@@ -0,0 +1,20 @@
+/*----------------------------------------------------------------------------*/
+/* 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "frc/buttons/Button.h"
+
+using namespace frc;
+
+void Button::WhenPressed(Command* command) { WhenActive(command); }
+
+void Button::WhileHeld(Command* command) { WhileActive(command); }
+
+void Button::WhenReleased(Command* command) { WhenInactive(command); }
+
+void Button::CancelWhenPressed(Command* command) { CancelWhenActive(command); }
+
+void Button::ToggleWhenPressed(Command* command) { ToggleWhenActive(command); }