E3D Titan Extruder with differential IR sensor mount for Prusa i3

This is a remix of the [E3D Titan Extruder with Sensor Mount](http://www.thingiverse.com/thing:1552022) remixed from [X Carriage](http://www.thingiverse.com/thing:1310161).
I added a small holes in carriage to simplify zip ties insertion, and designed sensor mount for [David Crocker's - Mini height sensor board](https://miscsolutions.wordpress.com/mini-height-sensor-board/).