Improved OpenAstroGuider scope

This is an improved version of the already great OpenAstroGuider and mounts to the new aluminium base. Whats new:

- Added thread between front and mid part to simplify focusing and make it more precise
- Lens hood holds the lens now (instead of friction only which was dependant on 3d printer tolerances and other factors)
- Made new 20x20 extrusion holders which can be mounted without the need to disassembly the main camera mount
- More precise guide camera sensor mounting improves polar alignment and guiding
- Camera sensor mounted without screws now
- Supporting many different camera modules as long as they have have same screw holes
- Reduced overall required screws amount
- multiple further small improvements

What you'll need:
- Achromatic lens with 50mm diameter and 182,8 focal lenght
- Camera sensor performing well in low light (e.g. AR0130 or IMX290). Monochrome sensor recommended.
- 2 x M4x8 screws
- 2 x M4 t-nuts
- 4 x M3x12 screws
- 2 x M3 hex nuts

Printe