Replicator 2X E3D-v6 upgrade - adjustable

Based on the awesome work by cadsys, but with a few tweaks and improvements.

The extruder mount is slightly modified to take a wider range of extruders, including the cheap chinese aluminium ones I had on hand. The hot end mount is now one piece as I found it hard to get the clip on fan mounts to sit in the right spot without them sliding around. The hot ends are also easily height adjustable with a single locking screw to slide them up and down. The catch is that the hotend mount now require