Extruder Block Top Plate Enhanced Upgrade for Dual Extrusion

This design (based on user toreg's [original design](http://www.thingiverse.com/thing:26679)) enables consistent filament feeding by creating enough room for both extruders to use the ["Minimalistic MK8 Upgrade"](http://www.thingiverse.com/thing:28241) by user emmett in tandem with my ["Spring Enhancer / Spring Compressor"](http://www.thingiverse.com/thing:604924). The original plate that ships with the Replicator Dual is a little too wide, which obstructs the range of motion of the Minimalistic