Kossel XL upgrade: carriage v2018 for print volume height increase up to 326 mm

See the upgraded design: https://www.thingiverse.com/thing:4049092

This carriage allows to gain more print volume - height up to 326 mm by
1. moving the tensioner from the top of the rail to the carriage and
2. moving the arms higher, allowing the arm to tuch the ceil of the printer



This carriage allows to gain more precision due to exact belt guidance

ATTENTION - IDENTIFIED PROBLEMS:
- lower endstop mount is needed, see the files attached in the comments