Add stack action.

This one's pretty simple...

I also removed the elevator_normal_height constant and replaced
it with a constant for how tall a tote is. Upon further
consideration, this made more sense and seemed more useful.

Change-Id: I4a7247b9e563b1c49cf853b7b05371be172aa500
diff --git a/frc971/constants.h b/frc971/constants.h
index ac6f315..18e85ae 100644
--- a/frc971/constants.h
+++ b/frc971/constants.h
@@ -36,6 +36,9 @@
   // The ratio from the pot shaft to the claw joint.
   double claw_pot_ratio;
 
+  // How tall a tote is in meters.
+  double tote_height;
+
   // The gear ratios from motor shafts to the drivetrain wheels for high and low
   // gear.
   double low_gear_ratio;
@@ -105,8 +108,6 @@
 
     // How high the elevator has to be before we start zeroing the arm.
     double arm_zeroing_height;
-    // The height at which the fridge should hang out by default.
-    double normal_height;
   };
   Fridge fridge;