Don't show app intro again after recomposition

[sunkup]

Purpose

The app intro replays after finish, when changing between dark and light theme or rotating the screen. It should not do that.

Short description

The problem is that we need to continuously consume the showAppIntro flow in order to start the app intro as soon as possible, but only want to do so once and not on every recomposition. There might be a cleaner way, but simply to

• remember the launched state across recomposition
• use rememberSaveable instead of remember to survive configuration changes (like screen rotation)

works just fine.

Checklist

• The PR has a proper title, description and label.
• I have self-reviewed the PR.
• I have added documentation to complex functions and functions that can be used by other modules.
• I have added reasonable tests or consciously decided to not add tests.

[ArnyminerZ]

Looks good to me, and it's simple enough. Though I would probably add a comment or something, since otherwise we might forget why this is here, and remove it at some point