1. Re-created all 3D print files in FreeCAD for easier modification by others. 
   Todo: Export individual STL, update instructions

2. In 'modules_tracking/common_tracking_classes.DescribeLargestObject' I changed
   the datatype from unint16 to int16 as it seemed I was getting overflow errors
   in one of my rigs. Unclear why this didn't show up before...

3. reorganized .gitignore file