Use simctl to add photos to the simulator in Xcode >=6

This is a bit of a lengthy change, but to use simctl reliably we need to boot the sim, add the photo, then shut it down again. If you don't shut down then you get a nasty crash which takes down all running apps and relaunches Finder. (I haven't yet filed a radar with Apple about that, I want to create a minimal repro case first.)