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.

wpilibNewCommands/src/main/native/include/frc2/command/SubsystemBase.h

@@ -0,0 +1,68 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 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/smartdashboard/Sendable.h>
+#include <frc/smartdashboard/SendableHelper.h>
+
+#include <string>
+
+#include "Subsystem.h"
+
+namespace frc2 {
+/**
+ * A base for subsystems that handles registration in the constructor, and
+ * provides a more intuitive method for setting the default command.
+ */
+class SubsystemBase : public Subsystem,
+                      public frc::Sendable,
+                      public frc::SendableHelper<SubsystemBase> {
+ public:
+  void InitSendable(frc::SendableBuilder& builder) override;
+
+  /**
+   * Gets the name of this Subsystem.
+   *
+   * @return Name
+   */
+  std::string GetName() const;
+
+  /**
+   * Sets the name of this Subsystem.
+   *
+   * @param name name
+   */
+  void SetName(const wpi::Twine& name);
+
+  /**
+   * Gets the subsystem name of this Subsystem.
+   *
+   * @return Subsystem name
+   */
+  std::string GetSubsystem() const;
+
+  /**
+   * Sets the subsystem name of this Subsystem.
+   *
+   * @param subsystem subsystem name
+   */
+  void SetSubsystem(const wpi::Twine& name);
+
+  /**
+   * Associate a Sendable with this Subsystem.
+   * Also update the child's name.
+   *
+   * @param name name to give child
+   * @param child sendable
+   */
+  void AddChild(std::string name, frc::Sendable* child);
+
+ protected:
+  SubsystemBase();
+};
+}  // namespace frc2