CTC i3 e3D mount (with SN04)

Remixed form JackWaterfall's very neat solution.

I did find a few issues with this version on my printer (a CTC i3 clone)

1. None of the mounting holes lined up with the existing mount points...
2. The SN04 proximity mount didn't allow the sensor to be lowered enough to trigger
3. The SN04 mount also hit the RHS Z-Axis on full movement.

So, I have remixed the mount (made a non SN04 version too)

- To use the existing CTC mount screw positions would have meant the screws would have been in the main body of the 'neck' of the e3D mount. so I've made two new holes in the CTC back plate and altered the e3D mount to give a nice working compromise.

- The SN04 sensor now has more than enough adjustment (with nut slots on the rear to hold the mount screws in place but still allow adjustment).

- The sensor position is also moved across to the left to get the sensor closer to the nozzle and allow more X-axis travel.

- The front plate mounted fan makes adjustment of the senso