Camera Mount for Raspberry Pi camera on 2020 Extrusion

I have created three new parts:
- a new base plate that is mounted beside the 2020 bar instead of on top of it;
- a new camera mount that fits my Raspberry Pi camera module;
- a modified version (camera_mount_2.stl) of [Raspberry pi camera case/enclosure](https://www.thingiverse.com/thing:92208) that fits the mounting

The base plate is mounted to the printer with two M4 screws and hammer nuts.

Print a [Bottom-Holder.stl and 2_Glied.stl](https://www.thingiverse.com/thing:2426231)
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