Cable clip for 2020 extrusion frame

Customizable cable clip for 2020 extrusion. Inspired by http://www.thingiverse.com/thing:1150396/

[27-11-2015] Updated to version 2.1. Now gap orientation can be changed. Or you can make clip without a gap.
[29-11-2015] Version 2.2. Now it better fits the extrusion. Also added parameter to fine tune the toughness.

Notes:
Not all variations of configurations can be valid.
Customizer can display some glitches in preview. They will not be there after rendering.