Snackbar to swipe

[JesseScott]

I want to show a Snackbar if the user has not been past the first page yet.
It should read from DataStore (and write to DataStore if the user does navigate).

[JesseScott]

Fix #53 first for better reliability / determinism of the usage.

[JesseScott]

Use DataStore
https://developer.android.com/jetpack/androidx/releases/datastore

[google-labs-jules]

Jules is on it. When finished, you will see another comment and be able to review a PR.

[google-labs-jules]

Ready for a review! A PR has been created.