prusa i3 X-carriage v1.0

[Open it in customizer](http://www.thingiverse.com/apps/customizer/run?thing_id=2037492)
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slightly modified

1. added cable chain with end chain holders
2. idler: corrected bearing holes
3. carriage:
- splitted for 3 parts for no cable tights version
- holes added
4. motor: added mount holes

middle carriage part need support with 30% grid