Vertex K8400 E3Dv6 Single mount

Inspired by rrekwa's (http://www.thingiverse.com/thing:750821) and others' designs for dual E3D T-bar style mount I created one more suited for single extrusion. This design allows you to have the E3D fan pointing back allowing for no loss of build area.

It also lowers the Vertex small fan and places it closer to the hot-end.

##### Needed
- 4 M3 long machine screws and locking nuts
- 3 M3 20 mm machine screws and nuts for the clamp.

##### Mounting the main piece to the carriage cla