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/BuiltInAccelerometer.h

@@ -7,13 +7,8 @@
 
 #pragma once
 
-#include <memory>
-#include <string>
-
-#include "LiveWindow/LiveWindowSendable.h"
 #include "SensorBase.h"
 #include "interfaces/Accelerometer.h"
-#include "networktables/NetworkTableEntry.h"
 
 namespace frc {
 
@@ -22,12 +17,9 @@ namespace frc {
  *
  * This class allows access to the roboRIO's internal accelerometer.
  */
-class BuiltInAccelerometer : public Accelerometer,
-                             public SensorBase,
-                             public LiveWindowSendable {
+class BuiltInAccelerometer : public SensorBase, public Accelerometer {
  public:
   explicit BuiltInAccelerometer(Range range = kRange_8G);
-  virtual ~BuiltInAccelerometer() = default;
 
   // Accelerometer interface
   void SetRange(Range range) override;
@@ -35,16 +27,7 @@ class BuiltInAccelerometer : public Accelerometer,
   double GetY() override;
   double GetZ() override;
 
-  std::string GetSmartDashboardType() const override;
-  void InitTable(std::shared_ptr<NetworkTable> subtable) override;
-  void UpdateTable() override;
-  void StartLiveWindowMode() override {}
-  void StopLiveWindowMode() override {}
-
- private:
-  nt::NetworkTableEntry m_xEntry;
-  nt::NetworkTableEntry m_yEntry;
-  nt::NetworkTableEntry m_zEntry;
+  void InitSendable(SendableBuilder& builder) override;
 };
 
 }  // namespace frc