Bottom piece for Dyson Fan

Modified bottom piece for Dyson Fan: http://www.thingiverse.com/thing:1645081
Changes from original:
- Removed some edges on the top to reduce support usage.
- Added holes to the bottom to reduce warping.
- Increased bottom thickness from 1.5mm to 2mm.
- Added 2mm height to fan slot to allow the use of Noctua fan with dampers.
- Added a hole on each side for panel mount DC socket.