Mobile stand

I've modified this file to improve performance. The original link was as below.
http://www.thingiverse.com/thing:71317/#comments

Improves
- Removed washer
- re-size the base width from 30mm to 50mm
- change screw holes diameter
- change tilting angle form 105 to 150 degree (each step 15 degree)

Screw: recommend
Flat head Phillips screw (3mm diameter)