CR2032 Battery 3D Files

Hello again!

I created CAD files for the PRT-00338 (Coin Cell CR2032 Battery), as well as provided renderings for it. Also, there is a small change to the .gitignore to ignore FreeCAD's backup files.

The only thing that I thought was a bit off was the size of the 1000x STL file, which is nearly 0.1 GB. I thought it would be a bit smaller, and I'm not sure if it is normal for FreeCAD to generate such large files. I'll look into it, and add another commit when I figure out if the file size is normal.

Thanks,
Blue Ice