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/SpeedControllerGroup.h

@@ -10,15 +10,17 @@
 #include <functional>
 #include <vector>
 
+#include "SmartDashboard/SendableBase.h"
 #include "SpeedController.h"
 
 namespace frc {
 
-class SpeedControllerGroup : public SpeedController {
+class SpeedControllerGroup : public SendableBase, public SpeedController {
  public:
   template <class... SpeedControllers>
   explicit SpeedControllerGroup(SpeedController& speedController,
                                 SpeedControllers&... speedControllers);
+  ~SpeedControllerGroup() override = default;
 
   void Set(double speed) override;
   double Get() const override;
@@ -28,6 +30,8 @@ class SpeedControllerGroup : public SpeedController {
   void StopMotor() override;
   void PIDWrite(double output) override;
 
+  void InitSendable(SendableBuilder& builder) override;
+
  private:
   bool m_isInverted = false;
   std::vector<std::reference_wrapper<SpeedController>> m_speedControllers;