Added `currentIndex` property to photo browser and a `photoBrowser:didDisplayPhotoAtIndex:` delegate method
Added readonly properties to MWPhoto to access the photo's origin URL or file path
Now preserves the visibility of the nag bar on the previous view controller.
Added option to set whether or not the navigation arrows are visible.

Conflicts:
	MWPhotoBrowser/Classes/MWPhotoBrowser.h
Project: Updated settings and architectures. (Xcode 4.6, armv7/s)
Updated project to use ARC
Removed depreciated status bar method call.
Updated SDWebImage (63178bd) and changed MWPhoto to use new completion block instead of delegate.
Demo: Updated project settings.
MWPhoto: Added SDWebImageOperation for cancelling download.
Switch SDWebImage to git submodule
Merge from https://github.com/swaterfall/MWPhotoBrowser.git