Cleaned up robot startup and cleanup/shutdown code (#77)

Cleaned up RobotBase, removed singleton list from SensorBase, and removed unused typedefs and NULL_TASK macro from HAL's Task.hpp. Making the robot class instance static fixed non-POD statics used by the instance during destruction from being destroyed first.

wpilibc/sim/src/DriverStation.cpp

@@ -51,8 +51,6 @@ DriverStation::DriverStation() {
   joysticks[5] = msgs::FRCJoystickPtr(new msgs::FRCJoystick());
   joysticksSub[5] = MainNode::Subscribe(
       "~/ds/joysticks/5", &DriverStation::joystickCallback5, this);
-
-  AddToSingletonList();
 }
 
 /**