Add shouldDelete*At methods to swipe cell delegates, invoke on swipe animation completion

[p4checo]

Currently both SwipeCollectionViewCell and SwipeTableViewCell automatically delete the cells on swipeController(:didDeleteSwipeableAt:) and don't allow any customization, like what's allowed in other similar methods.

While on most scenarios the default behavior is desired, there are some scenarios where users might want to control how the deletion is effectively made on the container (CollectionView or TableView). Some examples are:

• Data-driven setups that use diffing
• Customize the deletion animation (table view)

To achieve that, a new delegate method was added to both the SwipeCollectionViewCellDelegate and SwipeTableViewCellDelegate to allow customizing the deletion on the container, having the current implementations as the default in protocol extensions.

Following the above changes to the cell deletion flow on swipe completion, the actual cell deletion trigger was moved to the animation completion so that we wait for the swipe animation to complete before actually triggering the cell removal.

To prevent visual artifacts, the reset calls in the animation completion were moved to the prepareForReuse of each cell, achieving the same result.

Changes

• Add new collectionView(:shouldDeleteItemAt:) delegate method to SwipeCollectionViewCellDelegate, and invoke it on SwipeCollectionViewCell.swipeController(:didDeleteSwipeableAt:).

• Add new tableView(:shouldDeleteRowAt:) delegate method to SwipeTableViewCellDelegate and invoke it on SwipeTableViewCell.swipeController(:didDeleteSwipeableAt:).

• Invoke swipeController(:didDeleteSwipeableAt:) delegate call on delete animation completion

• Remove reset logic from SwipeController's delete animation completion closure, moving it to cell's prepareForReuse.