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/y2018/control_loops/superstructure/superstructure_output.fbs b/y2018/control_loops/superstructure/superstructure_output.fbs
index f4d62da..1055222 100644
--- a/y2018/control_loops/superstructure/superstructure_output.fbs
+++ b/y2018/control_loops/superstructure/superstructure_output.fbs
@@ -3,38 +3,38 @@
 table IntakeVoltage {
   // Voltage of the motors on the series elastic on one side (left or right) of
   // the intake.
-  voltage_elastic:double;
+  voltage_elastic:double (id: 0);
 
   // Voltage of the rollers on one side (left or right) of the intake.
-  voltage_rollers:double;
+  voltage_rollers:double (id: 1);
 }
 
 table Output {
   // Voltage sent to the parts on the left side of the intake.
-  left_intake:IntakeVoltage;
+  left_intake:IntakeVoltage (id: 0);
 
   // Voltage sent to the parts on the right side of the intake.
-  right_intake:IntakeVoltage;
+  right_intake:IntakeVoltage (id: 1);
 
   // Voltage sent to the motors on the proximal joint of the arm.
-  voltage_proximal:double;
+  voltage_proximal:double (id: 2);
 
   // Voltage sent to the motors on the distal joint of the arm.
-  voltage_distal:double;
+  voltage_distal:double (id: 3);
 
   // Voltage sent to the hanger.  Positive pulls the robot up.
-  voltage_winch:double;
+  voltage_winch:double (id: 4);
 
   // Clamped (when true) or unclamped (when false) status sent to the
   // pneumatic claw on the arm.
-  claw_grabbed:bool;
+  claw_grabbed:bool (id: 5);
 
   // If true, release the arm brakes.
-  release_arm_brake:bool;
+  release_arm_brake:bool (id: 6);
   // If true, release the hook
-  hook_release:bool;
+  hook_release:bool (id: 7);
   // If true, release the forks
-  forks_release:bool;
+  forks_release:bool (id: 8);
 }
 
 root_type Output;