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.inc

@@ -12,6 +12,12 @@ namespace frc {
 template <class... SpeedControllers>
 SpeedControllerGroup::SpeedControllerGroup(
     SpeedController& speedController, SpeedControllers&... speedControllers)
-    : m_speedControllers{speedController, speedControllers...} {}
+    : m_speedControllers{speedController, speedControllers...} {
+  for (auto& speedController : m_speedControllers)
+    AddChild(&speedController.get());
+  static int instances = 0;
+  ++instances;
+  SetName("SpeedControllerGroup", instances);
+}
 
 }  // namespace frc