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/cpp/IterativeRobotBase.cpp

@@ -12,6 +12,7 @@
 #include <HAL/HAL.h>
 #include <llvm/raw_ostream.h>
 
+#include "Commands/Scheduler.h"
 #include "LiveWindow/LiveWindow.h"
 
 using namespace frc;
@@ -191,4 +192,5 @@ void IterativeRobotBase::LoopFunc() {
     TestPeriodic();
   }
   RobotPeriodic();
+  LiveWindow::GetInstance()->UpdateValues();
 }