`manga.release` shouldn't be persisted

[agilgur5]

Because "Today" or "Yesterday" is a relative date and becomes out-of-date very quickly. Not persisting it depends on https://github.com/agilgur5/mst-persist/pull/16 .

That being said, we could add some logic to just not render it if the manga is a favorited manga for now, which fixes the most confusing part of the bug (having your manga say it was updated "Today" when it was actually released several days ago). manga.release was really only meant for latest manga, and I believe it's only persisted when it a favorite overlaps with a latest (as I think the updated date is only available on the latest page).

Sometimes manga.release is an actual date, and then it appears in gray, which is actually interesting (though could still be out of date). An interesting feature could be instead to display manga.chapters[0].date when there are no new unread chapters; I think that's better/more informative than just showing nothing. And thanks to #24 's auto-fetch chapters logic, it is always up-to-date (except when no internet connection) for favorited mangas. We could also update manga.release to just be a cached version of manga.chapters[0].date as well. For latest manga, their chapters likely haven't been fetched yet, so they should still display "Today" / "Yesterday".

In theory, there's a different fix that actually isn't as difficult (but would likely still require a migration), which is just to change manga.release to types.maybe(types.date) and parse "Today" or "Yesterday" (if it's only those two, that is relatively easy)