5b set overview

There's still stuff to do but the basic functionality for seeing all pictures in a set and zooming in on a picture exists. 
Consider changing this to `[NSMutableArray array]`. Although ARC is now part of almost every single ios program, it's good to follow common idioms;

Check this http://stackoverflow.com/questions/5423211/difference-between-nsmutablearray-array-vs-nsmutablearray-alloc-init if you're curious about the difference.