Log gear/shifting info in drivetrain status instead of seperate structs

Change-Id: Ib25174051fab63ec7b453da02ddf5f0a12e0145d
diff --git a/frc971/control_loops/drivetrain/polydrivetrain.h b/frc971/control_loops/drivetrain/polydrivetrain.h
index 570b87f..070b7eb 100644
--- a/frc971/control_loops/drivetrain/polydrivetrain.h
+++ b/frc971/control_loops/drivetrain/polydrivetrain.h
@@ -66,6 +66,12 @@
 
   double goal_left_velocity_ = 0.0;
   double goal_right_velocity_ = 0.0;
+
+  // Stored from the last iteration, for logging shifting logic.
+  double left_motor_speed_ = 0.0;
+  double right_motor_speed_ = 0.0;
+  double current_left_velocity_ = 0.0;
+  double current_right_velocity_ = 0.0;
 };
 
 }  // namespace drivetrain