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/I2C.h

@@ -9,7 +9,7 @@
 
 #include <stdint.h>
 
-#include "SensorBase.h"
+#include "ErrorBase.h"
 
 enum HAL_I2CPort : int32_t;
 
@@ -21,12 +21,12 @@ namespace frc {
  * This class is intended to be used by sensor (and other I2C device) drivers.
  * It probably should not be used directly.
  */
-class I2C : SensorBase {
+class I2C : public ErrorBase {
  public:
   enum Port { kOnboard = 0, kMXP };
 
   I2C(Port port, int deviceAddress);
-  virtual ~I2C();
+  ~I2C() override;
 
   I2C(const I2C&) = delete;
   I2C& operator=(const I2C&) = delete;