Scalar - Bowden to Direct Drive Adaptator

This part is an adapator to convert a Bowden system into a Direct drive one.

It is designed to be screwed on top of a AllInOne hot end support block.
There are 2 versions depending on the X carriage size:
* 1 for Scalar XL
* 1 for Scalar M

## Updates:
2016.01.19: update direct drive extruder body to fit M4 screw heads instead of M4 nuts hex fittings.
2015.12.28 - update the models, add some special parts called "ptfe" with a 7mm inner hole for a 6mm ptfe tube to be inserted inside. A