Simple UI Configuration for INSPhotosViewController and INSPhotosOverlayView

[blinover]

Hi

I add UI configuration file for INSPhotosViewController.

Now you can specify:

• backgroundColor
• activityIndicatorColor
• navigationTitleTextColor
• shadowStartColor
• shadowEndColor
• shadowHidden
• rightBarButtonHidden
• leftBarButtonHidden

Code sample:

func collectionView(collectionView: UICollectionView, didSelectItemAtIndexPath indexPath: NSIndexPath) {
    let cell = collectionView.cellForItemAtIndexPath(indexPath) as! ExampleCollectionViewCell
    let currentPhoto = photos[indexPath.row]
    
    let configuration = INSConfiguration()
    configuration.backgroundColor = .white
    configuration.activityIndicatorColor = .blue
    configuration.shadowHidden = true
    configuration.rightBarButtonHidden = true
    configuration.leftBarButtonHidden = true
    configuration.navigationTitleTextColor = .green
    
    let galleryPreview = INSPhotosViewController<INSPhoto>(photos: photos, initialPhoto: currentPhoto, referenceView: cell, configuration: configuration)

    galleryPreview.referenceViewForPhotoWhenDismissingHandler = { [weak self] photo in
        if let index = self?.photos.indexOf({$0 === photo}) {
            let indexPath = NSIndexPath(forItem: index, inSection: 0)
            return collectionView.cellForItemAtIndexPath(indexPath) as? ExampleCollectionViewCell
        }
        return nil
    }
    presentViewController(galleryPreview, animated: true, completion: nil)
}

Also i added this sample to README.