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/AnalogTriggerOutput.h

@@ -50,7 +50,7 @@ class AnalogTriggerOutput : public DigitalSource {
   friend class AnalogTrigger;
 
  public:
-  virtual ~AnalogTriggerOutput();
+  ~AnalogTriggerOutput() override;
   bool Get() const;
 
   // DigitalSource interface
@@ -59,6 +59,8 @@ class AnalogTriggerOutput : public DigitalSource {
   bool IsAnalogTrigger() const override;
   int GetChannel() const override;
 
+  void InitSendable(SendableBuilder& builder) override;
+
  protected:
   AnalogTriggerOutput(const AnalogTrigger& trigger,
                       AnalogTriggerType outputType);