Problems with running the examples - stl files

[Serafadam]

Hey, so I had some problems with running the bullet python examples, the source of those problems is that thought the stl files have beenample moved, urdf files haven't really been updated (rplidar_main.stl is missing and some tags point to foot.stl in STL folder (which has been removed). I can make a PR to fix this issues if you want 🙂