Titan E3Dv6 & Volcano fan mounts

This is a remix of Zeeflyboys excellent magnetic combo fan mount + cooling duct system for the E3D; simple, elegent and effective allowing quick nozzle or hot-end changes.

I had 3 teeny issues to overcome:
1 - the original duct didn't fit into the mouth of my 50mm fan. Fixed with a resize to suit what I had; YMMV.
2 - the 8x2mm N52 magnets need the sockets resized a smidge, but even with a tight press fit they were so strong they kept pulling out of the socket in the duct. I edited the duct