Timing Belt X GT2, Printrbot Simple V2

**This will work for both V2 designs (with & w/o string tension)**

In response to multiple requests I have developed this GT2 timing belt conversion for the X axis of the Printrbot Simple. This thing is similar to my original http://www.thingiverse.com/thing:191706

Differences are:
- Use GT2 belt & pulley instead of the MXL
- Use 608 Bearings instead of R2
- Raises print bed 6.5mm

Benefits:
- GT2 tooth form
- Common 608 Bearings

Drawbacks:
- Bearing Caps have very t