Simplify Sendable interface (#1864)

This removes the name and subsystem from individual objects, and instead
puts this data into a new singleton class, SendableRegistry.  Much of
LiveWindow has been refactored into SendableRegistry.

In C++, a new CRTP helper class, SendableHelper, has been added to provide
move and destruction functionality.

Shims for GetName, SetName, GetSubsystem, and SetSubsystem have been added
to Command and Subsystem (both old and new), and also to SendableHelper to
prevent code breakage.

This deprecates SendableBase in preparation for future removal.

wpilibc/src/main/native/include/frc/livewindow/LiveWindow.h

@@ -9,13 +9,10 @@
 
 #include <memory>
 
-#include <wpi/Twine.h>
-#include <wpi/deprecated.h>
-
-#include "frc/smartdashboard/Sendable.h"
-
 namespace frc {
 
+class Sendable;
+
 /**
  * The LiveWindow class is the public interface for putting sensors and
  * actuators on the LiveWindow.
@@ -33,44 +30,6 @@ class LiveWindow {
    */
   static LiveWindow* GetInstance();
 
-  /**
-   * Add a component to the LiveWindow.
-   *
-   * @param sendable component to add
-   */
-  void Add(std::shared_ptr<Sendable> component);
-
-  /**
-   * Add a component to the LiveWindow.
-   *
-   * @param sendable component to add
-   */
-  void Add(Sendable* component);
-
-  /**
-   * Add a child component to a component.
-   *
-   * @param parent parent component
-   * @param child child component
-   */
-  void AddChild(Sendable* parent, std::shared_ptr<Sendable> component);
-
-  /**
-   * Add a child component to a component.
-   *
-   * @param parent parent component
-   * @param child child component
-   */
-  void AddChild(Sendable* parent, void* component);
-
-  /**
-   * Remove the component from the LiveWindow.
-   *
-   * @param sendable component to remove
-   * @return true if the component was removed; false if it was not present
-   */
-  bool Remove(Sendable* component);
-
   /**
    * Enable telemetry for a single component.
    *