Improved Bluetooth Camera Slider parts

This is a remix of the Bluetooth Motorized Camera Slider from Adafruit.

I changed the bearing mount part by adding a slot for mounting to the leg. This allows you to adjust for better belt tension. I also adjusted the pin that the skate bearing goes on. Previously it was 8mm which is same diameter of the skate bearing hole. This made it very difficult to put the bearing on without breaking the peg if the printer wasn't perfectly dialed in. It is now a 7.8mm peg.

I also adjusted the holes