Sparkfun XRP chassis altered for easier printing without supports

The original XRP chassis is cool, but not that well optimized for printing. It requires substantial supports and uses lots of fillets tangent to the print bed, which causes very steep overhangs that print poorly. 

To improve the printability, I changed the large fillets against the bed to chamfers, which reduces the overhang steepness, but doesn't change the functionality. 

I also changed the center area that holds the batteries and XRP mainboard quite a bit, taking it from a monolithic shape that requires support in multiple areas and breaking it into a couple separate pieces that all print without support. The pieces snap together and don't require any glue or screws. 

There are a few other minor changes as well, some small chamfers here and there, etc.