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/BuiltInAccelerometer.h

@@ -1,5 +1,5 @@
 /*----------------------------------------------------------------------------*/
-/* Copyright (c) 2014-2018 FIRST. All Rights Reserved.                        */
+/* Copyright (c) 2014-2019 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.                                                               */
@@ -9,18 +9,22 @@
 
 #include "frc/ErrorBase.h"
 #include "frc/interfaces/Accelerometer.h"
-#include "frc/smartdashboard/SendableBase.h"
+#include "frc/smartdashboard/Sendable.h"
+#include "frc/smartdashboard/SendableHelper.h"
 
 namespace frc {
 
+class SendableBuilder;
+
 /**
  * Built-in accelerometer.
  *
  * This class allows access to the roboRIO's internal accelerometer.
  */
 class BuiltInAccelerometer : public ErrorBase,
-                             public SendableBase,
-                             public Accelerometer {
+                             public Accelerometer,
+                             public Sendable,
+                             public SendableHelper<BuiltInAccelerometer> {
  public:
   /**
    * Constructor.