change default resolution to that of my Air.. because I can
Refactor set_wallpaper so that it determines internally which platform we're on. Even though this is meant just for Mac OS X, let's keep the original Ubuntu code around just for posterity.
'Customer feedback' (or a friend I talked to) said it could be distracting to have the wallpaper changing multiple times a day. I agreed, and figured it is called 'Picture of the DAY' for a reason. So we'll keep image scroll disabled, but again keep the funciton around just in case we want it later.
Fix find_resolution() to automatically determine screen resolution for OSX. Still needs to be fixed for when there are multiple screens attached.