J-head mount for RepRapPro Ormerod

Parts for mounting a common J-head hotend on a RepRapPro Ormerod printer. The fan duct is an adaptation of an [existing design](http://www.thingiverse.com/thing:184055), modified with a different mount as well as angling the fan up a bit to make it lighter and smaller. The "cooling ring" has been cut off since it got in the way of the hotend.
It screws into the regular X carriage in place of the stock nozzle mount. The nozzle will be in the same X/Y spot as the original one, but about 20mm further down, which will limit build height. It has mounts for [dc42's sensor board](https://github.com/dc42/OrmerodSensorBoard/), as well as a modified sensor pad for X homing. Since the nozzle and sensor are about 20mm further down relative to the Z carriage, the pad is dropped down as well.
All parts are licensed under CC BY-SA, except the sensor mount which is GNU GPL (in line with the part it is based on).