Mendel OpenX Carriage Bling2

This design improves on the last Bling Carriage by:
(a) adding captured M3 nut cavities for the tensioner(s)
(b)Adding some extra space for the belt to pass thru!
(c) most importantly!, on the non-tension side, add a flex member to ensure top+bottom bearing contact (reduce wobble about the x-axis)
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This is ALSO a drop-in replacement for the standard mendel x-carriage. It is is inspired by Buback's OpenX Carriage with the following mods:

1) Integrated belt tensioner
2) Fan mounting
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