Extruder YRUDS MK7 3mm for HTD3M belt - for E3D hotend

Changes:
- removed J-head mount
- centered filament hole
- centered whole extruder for Wade mount

Best with this mount - http://www.thingiverse.com/thing:148536

**Edit - 2013.12.08:** added version v2 with thicker motor mount part
**Edit - 2015.03.31:** added version v3 with even more thicker and stronger motor mount part