Prusa i3 MK3 Memory and Tool Holder

**UPDATED:** emancarrillo discovered that the bottom of the main piece wasn't flat. I've fixed the issue and re-uploaded as "Prusa_i3_MK3_Tool_Holder-Main_Fixed.stl". I verified in Slic3R that the first layer is now flat and encompasses the entire model.
** End Update**

I found Premolo1993's SD holder for the Prusa MK3 (https://www.thingiverse.com/thing:3236372) and loved the idea of a holder that clips to the frame from behind and above the power supply.

But I wanted it to also hold som