Made Velocity Shooter loop such that it should run.

Currently, all it builds and passes all the tests. I need to go in and check to see if there are any more tests I should add.
diff --git a/frc971/control_loops/state_feedback_loop.h b/frc971/control_loops/state_feedback_loop.h
index ff5e9d8..cc11dfc 100644
--- a/frc971/control_loops/state_feedback_loop.h
+++ b/frc971/control_loops/state_feedback_loop.h
@@ -294,11 +294,15 @@
 
   // update_observer is whether or not to use the values in Y.
   // stop_motors is whether or not to output all 0s.
-  void Update(bool update_observer, bool stop_motors) {
+  // U_add is for the bot3 shooter velocity control, where a constant
+  // must be added to get a good U.
+  void Update(bool update_observer, bool stop_motors,
+              Eigen::Matrix<double, number_of_inputs, 1> U_add =
+              Eigen::Matrix<double, number_of_inputs, 1>::Zero()) {
     if (stop_motors) {
       U.setZero();
     } else {
-      U = U_uncapped = K() * (R - X_hat);
+      U = U_uncapped = K() * (R - X_hat) + U_add;
       CapU();
     }