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.

wpilibcExamples/src/main/cpp/templates/commandbased/Robot.cpp

@@ -83,7 +83,7 @@ public:
 
 	void TeleopPeriodic() override { frc::Scheduler::GetInstance()->Run(); }
 
-	void TestPeriodic() override { frc::LiveWindow::GetInstance()->Run(); }
+	void TestPeriodic() override {}
 
 private:
 	// Have it null by default so that if testing teleop it

wpilibcExamples/src/main/cpp/templates/iterative/Robot.cpp

@@ -60,7 +60,7 @@ public:
 
 	void TeleopPeriodic() {}
 
-	void TestPeriodic() { m_lw.Run(); }
+	void TestPeriodic() {}
 
 private:
 	frc::LiveWindow& m_lw = *LiveWindow::GetInstance();

wpilibcExamples/src/main/cpp/templates/timed/Robot.cpp

@@ -59,7 +59,7 @@ public:
 
 	void TeleopPeriodic() {}
 
-	void TestPeriodic() { m_lw.Run(); }
+	void TestPeriodic() {}
 
 private:
 	frc::LiveWindow& m_lw = *LiveWindow::GetInstance();