Quick start updates

[vladimir-trib]

DTCollectionViewManageable doesn't work with outlets like @IBOutlet weak var collectionView: UICollectionView!. Please, updates the Quick start documentation to use the following protocol DTCollectionViewNonOptionalManageable instead of the DTCollectionViewManageable for @outlet. Thanks.

[DenTelezhkin]

Hi! The readme was updated to reflect code for the 7.0.0-beta, that does not have DTCollectionViewNonOptionalManageable protocol anymore.

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