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/SmartDashboard/SmartDashboard.h

@@ -16,7 +16,6 @@
 
 namespace frc {
 
-class NamedSendable;
 class Sendable;
 
 class SmartDashboard : public SensorBase {
@@ -38,7 +37,7 @@ class SmartDashboard : public SensorBase {
   static void Delete(llvm::StringRef key);
 
   static void PutData(llvm::StringRef key, Sendable* data);
-  static void PutData(NamedSendable* value);
+  static void PutData(Sendable* value);
   static Sendable* GetData(llvm::StringRef keyName);
 
   static bool PutBoolean(llvm::StringRef keyName, bool value);