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/SendableBase.h

@@ -0,0 +1,44 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 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 <memory>
+#include <string>
+
+#include <support/mutex.h>
+
+#include "Sendable.h"
+
+namespace frc {
+
+class SendableBase : public Sendable {
+ public:
+  explicit SendableBase(bool addLiveWindow = true);
+  ~SendableBase() override;
+
+  using Sendable::SetName;
+
+  std::string GetName() const final;
+  void SetName(const llvm::Twine& name) final;
+  std::string GetSubsystem() const final;
+  void SetSubsystem(const llvm::Twine& subsystem) final;
+
+ protected:
+  void AddChild(std::shared_ptr<Sendable> child);
+  void AddChild(void* child);
+
+  void SetName(const llvm::Twine& moduleType, int channel);
+  void SetName(const llvm::Twine& moduleType, int moduleNumber, int channel);
+
+ private:
+  mutable wpi::mutex m_mutex;
+  std::string m_name;
+  std::string m_subsystem = "Ungrouped";
+};
+
+}  // namespace frc