Add empty NSPhotoLibraryUsageDescription
Add empty NSPhotoLibraryUsageDescription

Because we link against ReactiveObjC, which includes helpers for
wrapping `UIImagePickerController`, our binary is being rejected because
we don't specify a usage description. Hopefully an empty value for this
key will be sufficient to validate our binary.

faimin/Tropos,andreamazz/Tropos,thoughtbot/Tropos,andreamazz/Tropos,thoughtbot/Tropos,andreamazz/Tropos,thoughtbot/Tropos,faimin/Tropos,faimin/Tropos