Update LiveWindow to provide continuous telemetry. (#771)

LiveWindow.updateValues() is now called from IterativeRobotBase on every
loop iteration.  Telemetry for all WPILib classes is enabled by default;
it can be disabled for specific classes using LiveWindow.disableTelemetry(),
or all telemetry can be disabled using LiveWindow.disableAllTelemetry().

This necessitated changing the hook methodology into other classes to
be more property-based rather than each class providing multiple functions.
This had the benefit of reducing boilerplate and increasing consistency.

- Remove NamedSendable, add name to Sendable.

- Provide SendableBase abstract class.

- Deprecate LiveWindow addSensor/addActuator interfaces.

- Add LiveWindow support to drive classes.

- Add addChild() helper functions to Subsystem.

- Fix inheritance hierarchy.  Now only sensors inherit from SensorBase.
  Other devices inherit from some combination of SendableBase, ErrorBase, or
  nothing.

wpilibc/src/main/native/include/SmartDashboard/NamedSendable.h

@@ -1,29 +0,0 @@
-/*----------------------------------------------------------------------------*/
-/* Copyright (c) 2012-2017 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 <string>
-
-#include "SmartDashboard/Sendable.h"
-
-namespace frc {
-
-/**
- * The interface for sendable objects that gives the sendable a default name in
- * the Smart Dashboard.
- */
-class NamedSendable : public Sendable {
- public:
-  /**
-   * @return The name of the subtable of SmartDashboard that the Sendable object
-   *         will use
-   */
-  virtual std::string GetName() const = 0;
-};
-
-}  // namespace frc