Anti warp pad

This helps keep the corners from warping. Since the settings in Cura and others usually generate a bit more brim than necessary I designed this. Put as many as needed around your print, they easily twist off afterwards. Cura complains about overlapping parts but still generates perfectly fine gcode

I generally wait for the first layer to print and then put some tape over the pads. For that purpose I have uploaded the [improved and hollow pad](http://www.thingiverse.com/thing:1448758) which can be taped earlier.