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/Servo.h

@@ -7,12 +7,8 @@
 
 #pragma once
 
-#include <memory>
-#include <string>
-
 #include "SafePWM.h"
 #include "SpeedController.h"
-#include "networktables/NetworkTableEntry.h"
 
 namespace frc {
 
@@ -25,7 +21,6 @@ namespace frc {
 class Servo : public SafePWM {
  public:
   explicit Servo(int channel);
-  virtual ~Servo();
   void Set(double value);
   void SetOffline();
   double Get() const;
@@ -34,15 +29,7 @@ class Servo : public SafePWM {
   static double GetMaxAngle() { return kMaxServoAngle; }
   static double GetMinAngle() { return kMinServoAngle; }
 
-  void UpdateTable() override;
-  void StartLiveWindowMode() override;
-  void StopLiveWindowMode() override;
-  std::string GetSmartDashboardType() const override;
-  void InitTable(std::shared_ptr<nt::NetworkTable> subTable) override;
-
- protected:
-  nt::NetworkTableEntry m_valueEntry;
-  NT_EntryListener m_valueListener = 0;
+  void InitSendable(SendableBuilder& builder) override;
 
  private:
   double GetServoAngleRange() const { return kMaxServoAngle - kMinServoAngle; }