Aurora 90 battery clip

I quite liked the idea of [darthskids Snap in battery tray for Eachine Aurora 90](http://www.thingiverse.com/thing:2060438), but it didn't fit my batteries quite perfectly. So I recreated it in OpenSCAD, making the battery size easily changeable.

I've included two STLs, one matches the Turnigy nano-tech 2S 460mAh batteries, the other matches two Turnigy nano-tech 1S 750mAh. I'm using the second one because I'm still waiting for more 2S batteries and want to use the 1S batteries of my smaller quad in the meantime.