Use explicit flatbuffer IDs in y2017 and newer.

Non-explicit ids are risky.  We've seen backwards incompatible
changes...

Change-Id: Id6ceebe031ac80430191f367635d0e951c3d2cbc
diff --git a/y2019/control_loops/superstructure/superstructure_position.fbs b/y2019/control_loops/superstructure/superstructure_position.fbs
index 80a851e..86a615d 100644
--- a/y2019/control_loops/superstructure/superstructure_position.fbs
+++ b/y2019/control_loops/superstructure/superstructure_position.fbs
@@ -5,26 +5,26 @@
 table Position {
   // Input from pressure sensor in bar
   // 1 = 1 atm, 0 = full vacuum
-  suction_pressure:float;
+  suction_pressure:float (id: 0);
 
   // Position of the elevator, 0 at lowest position, positive when up.
-  elevator:frc971.PotAndAbsolutePosition;
+  elevator:frc971.PotAndAbsolutePosition (id: 1);
 
   // Position of wrist, 0 when up, positive is rotating toward the front,
   // over the top.
-  wrist:frc971.PotAndAbsolutePosition;
+  wrist:frc971.PotAndAbsolutePosition (id: 2);
 
   // Position of the intake. 0 when rollers are retracted, positive extended.
-  intake_joint:frc971.AbsolutePosition;
+  intake_joint:frc971.AbsolutePosition (id: 3);
 
   // Position of the stilts, 0 when retracted (defualt), positive lifts robot.
-  stilts:frc971.PotAndAbsolutePosition;
+  stilts:frc971.PotAndAbsolutePosition (id: 4);
 
   // True if the platform detection sensors detect the platform directly
   // below the robot right behind the left and right wheels.  Useful for
   // determining when the robot is all the way on the platform.
-  platform_left_detect:bool;
-  platform_right_detect:bool;
+  platform_left_detect:bool (id: 5);
+  platform_right_detect:bool (id: 6);
 }
 
 root_type Position;