Arm works

Added gravity and calibrated it.  Terifying...

Change-Id: I70babb1cd3b83ddd7a81f06fb2a75cefd55bcdb8
diff --git a/y2018/constants.h b/y2018/constants.h
index 73d485a..1c18bde 100644
--- a/y2018/constants.h
+++ b/y2018/constants.h
@@ -97,13 +97,13 @@
     ::frc971::constants::PotAndAbsoluteEncoderZeroingConstants zeroing;
     double potentiometer_offset;
   };
-  Proximal proximal;
+  Proximal arm_proximal;
 
   struct Distal {
     ::frc971::constants::PotAndAbsoluteEncoderZeroingConstants zeroing;
     double potentiometer_offset;
   };
-  Distal distal;
+  Distal arm_distal;
 
   const char *vision_name;