Improve gyro zeroing

Instead of using a single large data chunk for zeroing, collect multiple
shorter samples that we then gradually accumulate.

Change-Id: I5496a7c47a703764fcd0f5b1498ef080e9b30fe9
diff --git a/frc971/zeroing/BUILD b/frc971/zeroing/BUILD
index a2b908b..75d610a 100644
--- a/frc971/zeroing/BUILD
+++ b/frc971/zeroing/BUILD
@@ -35,6 +35,8 @@
     ],
     deps = [
         ":averager",
+        "//frc971/control_loops:control_loops_fbs",
+        "//frc971/control_loops/drivetrain:drivetrain_status_fbs",
         "//frc971/wpilib:imu_fbs",
         "@com_github_google_glog//:glog",
         "@org_tuxfamily_eigen//:eigen",