KISS ESC tray and guard for ZMR250 or other quad

Designed a tray to hold four KISS ESCs for my ZMR250 miniquad, but it can also be used for other frames.

Weighs about 3gm, printed @ 0.2mm with 20% infill using Simplify3D.

##Rev 2015-01-18 (kissesc-holder-r5.stl)
- Cleaned up little angles on sides because they were unnecessary
- Added airflow holes via ribs (still refuse to add holes at bottom to prevent water splashing in from bottom