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/Commands/PIDCommand.h

@@ -54,8 +54,7 @@ class PIDCommand : public Command, public PIDOutput, public PIDSource {
   std::shared_ptr<PIDController> m_controller;
 
  public:
-  void InitTable(std::shared_ptr<nt::NetworkTable> subtable) override;
-  std::string GetSmartDashboardType() const override;
+  void InitSendable(SendableBuilder& builder) override;
 };
 
 }  // namespace frc