Some changes for real scrolling to initialIndex and using several galleries

When we using list of galleries it is handy to have public link on UIPhotoGalleryView's instance for identify concrete gallery in UIPhotoGalleryDataSource methods.

For real scrolling to initialIndex in UIPhotoGalleryViewController I added call of setInitialIndex:animated: from viewDidAppear:.

After poping UIPhotoGalleryViewController's instance I see previous image from vPhotoGallery above current viewController about a second in case of images count is more than 1 and current index is more than 0. To solve this issue I added "self.vPhotoGallery.hidden = YES" in "viewWillDisappear:".