Fruit picker attachment variable broom size and split design

I remixed attachment from Bozidor fruit picker to fit brooms of different sizes. I generated it from 18mm to 36mm diameter, but you can request other sizes. Hole is for 5mm screw, but 4mm or 3mm screw with big head will work. Single piece parts are named `picker_attachment_XY.stl`, where XY labels the brooms diameter.

I also added design splitted into 3 parts. This ways the individual features can be printed in correct orientation to gain strength locally and inside screws will also provide strength to the attachment as I have tested. Using glue alongside screws is recommended, but not necessary. You need two M3 12-14mm screws to join connector and joint and two M3 12-28mm screws to join broom part and connector. Split design parts are named `picker_attachment_split_joint.stl`, `picker_attachment_split_connector.stl` and `picker_attachment_split_broom_XY.stl`.

This picker attachment is remix and it needs the picker itself from [original fruit picker](https://www.thingiverse.com/