E3D v6 Hotend mount for Creality CR7, CR8, CR10. Support standard and Volcano heatblock

This is an update to my earlier design (see link at end for previous things)
The following has been improved:
- The part cooling fang, supporting a standard 40x40mm fan has been added. Part can be adjusted to accommodate the difference in height of normal heat block and Volcano heat block.

- The hotend cooling fan duct has been simplified
- The front part has been simplified and also to allow mounting of the cooling fang.
- Overall threading for all parts are now M3

2018-11-22
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