[appinio_swiper] General improvements

[ricardodalarme]

Description

This PR doesn't add any new features, but improves the code in a few aspects:

• Change the swipeType to be an enum instead of an int for type-safety
• Make all callbacks type-safe
• Replace useless containers
• Change the cards prop to be non-nullable as it is required

[ricardodalarme]

@bilalhamud can I get a review on my PRs?