Eclips3D Titan Gantry

This is a remix of [Rock75's Eclips3D Titan Gantry](https://www.thingiverse.com/thing:1598224) with a number of changes, many of which are to reduce the amount of print support. Some cable tie-downs have been added, and the bore for the oil-free bushings has been increased.

Last but not least, a provision to mount an [Escher3D Mini Differential IR height sensing board](https://miscsolutions.wordpress.com/mini-height-sensor-board/) has been added.

This will change the gantry's effective hei