Spring-loaded Thing-O-Matic Drive Block

Showin' love for the T-O-M.

Based on ivc's _Spring-loaded Replicator 1 Drive Block_, and coming full circle (more like ellipse) back to the Thing-O-Matic, this is a drive block that uses the Replicator 2 vitamin kit http://store.makerbot.com/drive-block-hardware-kit.html on the Mk 7 extruder.

**Changes**
* Removed 12mm from bottom to accomodate Mk 7 mounting block
* Changed the lever and base screw hole to accept _Replicator 2_ vitamins
* Changed bearing spindle to work with _Replic