Modified i3 parts

Modifications:

• Z axis motor end has been change to look nicer
  Z axis top rod holding length increased, end is now flared for easier insertion
  X motor end has holes in it for less warping while printing and less material use
  X carriage and extruder now have an extra hole for stability
  Cold end is a modified version of http://www.thingiverse.com/thing:28430 to fit an i3