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/SensorBase.h

@@ -7,8 +7,12 @@
 
 #pragma once
 
+#include <memory>
+
 #include "Base.h"
 #include "ErrorBase.h"
+#include "SmartDashboard/Sendable.h"
+#include "SmartDashboard/SendableBase.h"
 
 namespace frc {
 
@@ -18,10 +22,9 @@ namespace frc {
  * Stores most recent status information as well as containing utility functions
  * for checking channels and error processing.
  */
-class SensorBase : public ErrorBase {
+class SensorBase : public ErrorBase, public SendableBase {
  public:
   SensorBase() = default;
-  virtual ~SensorBase() = default;
 
   SensorBase(const SensorBase&) = delete;
   SensorBase& operator=(const SensorBase&) = delete;