Herculien XY end, snap-in bearing (WIP)

A remix of the XY ends designed for the Eustathios and Herculien reprap printers. Please note this is a work in progress and has not been tested extensively. Perceived benefits include:

1) The bearings have more freedom (more tolerant of misalignment). Smoother motion before running break in routine.

2) Uses this bearing from Robotdigg (http://www.robotdigg.com/product/451/Selfgraphite+10*14*30mm+Linear+Bearing) and the design could be adapted for Igus or Simplicity bearings.

3) Bearing