Raiscube A8R E3D V6 mount

This thing is inspired by the [design](https://www.thingiverse.com/thing:2099577) of TNS

An adaptation of the well-known E3D V6 hotend to the Raiscube A8R printer. This printer uses 49mm spacing for the X rails so direct use of things designed for Anet printers was not possible. Furthermore, I've already designed my own X belt tensioner, fan mount, semi-circular fan duct etc. for the original direct drive [upgrade](https://www.thingiverse.com/thing:3500653) which turned to be very good so I wanted to stay at the well-proven design :) Of course, all components were modified as at the end the whole assembly is very different. It incorporates already the little fan hook which addresses an issue I discovered on the above mentioned upgrade.

An already known issue: with the X limit switch mounted like this, we lose some 15-20mm of X dimension as the hotend is placed in the middle of the carriage rather then on the leftmost corner... For me it is not an issue yet as I'm printing on a mi