Explore how CellKit works in combination with DiffableDataSources

[mkj-is]

iOS 13 (macOS 10.15) diffable data sources still have complicated initialization. We should explore whether at least some parts of CellKit could be used with it.

• https://developer.apple.com/documentation/uikit/uicollectionviewdiffabledatasource
• https://developer.apple.com/documentation/uikit/nsdiffabledatasourcesnapshot
• https://developer.apple.com/documentation/uikit/uitableviewdiffabledatasource
• https://developer.apple.com/documentation/uikit/nsdiffabledatasourcesnapshotreference

[mkj-is]

Concept was explored here: https://github.com/futuredapp/narodni-muzeum-ios/pull/21