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/AnalogPotentiometer.h

@@ -8,12 +8,10 @@
 #pragma once
 
 #include <memory>
-#include <string>
 
 #include "AnalogInput.h"
-#include "LiveWindow/LiveWindowSendable.h"
+#include "SensorBase.h"
 #include "interfaces/Potentiometer.h"
-#include "networktables/NetworkTableEntry.h"
 
 namespace frc {
 
@@ -23,7 +21,7 @@ namespace frc {
  * units you choose, by way of the scaling and offset constants passed to the
  * constructor.
  */
-class AnalogPotentiometer : public Potentiometer, public LiveWindowSendable {
+class AnalogPotentiometer : public SensorBase, public Potentiometer {
  public:
   /**
    * AnalogPotentiometer constructor.
@@ -52,7 +50,7 @@ class AnalogPotentiometer : public Potentiometer, public LiveWindowSendable {
   explicit AnalogPotentiometer(std::shared_ptr<AnalogInput> input,
                                double fullRange = 1.0, double offset = 0.0);
 
-  virtual ~AnalogPotentiometer() = default;
+  ~AnalogPotentiometer() override = default;
 
   /**
    * Get the current reading of the potentiomer.
@@ -68,29 +66,11 @@ class AnalogPotentiometer : public Potentiometer, public LiveWindowSendable {
    */
   double PIDGet() override;
 
-  /*
-   * Live Window code, only does anything if live window is activated.
-   */
-  std::string GetSmartDashboardType() const override;
-  void InitTable(std::shared_ptr<nt::NetworkTable> subtable) override;
-  void UpdateTable() override;
-
-  /**
-   * AnalogPotentiometers don't have to do anything special when entering the
-   * LiveWindow.
-   */
-  void StartLiveWindowMode() override {}
-
-  /**
-   * AnalogPotentiometers don't have to do anything special when exiting the
-   * LiveWindow.
-   */
-  void StopLiveWindowMode() override {}
+  void InitSendable(SendableBuilder& builder) override;
 
  private:
   std::shared_ptr<AnalogInput> m_analog_input;
   double m_fullRange, m_offset;
-  nt::NetworkTableEntry m_valueEntry;
 };
 
 }  // namespace frc