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/PIDSubsystem.h

@@ -35,7 +35,7 @@ class PIDSubsystem : public Subsystem, public PIDOutput, public PIDSource {
   PIDSubsystem(double p, double i, double d);
   PIDSubsystem(double p, double i, double d, double f);
   PIDSubsystem(double p, double i, double d, double f, double period);
-  virtual ~PIDSubsystem() = default;
+  ~PIDSubsystem() override = default;
 
   void Enable();
   void Disable();
@@ -66,10 +66,6 @@ class PIDSubsystem : public Subsystem, public PIDOutput, public PIDSource {
  private:
   // The internal PIDController
   std::shared_ptr<PIDController> m_controller;
-
- public:
-  void InitTable(std::shared_ptr<nt::NetworkTable> subtable) override;
-  std::string GetSmartDashboardType() const override;
 };
 
 }  // namespace frc