Marquee based on ItemsRepeater

[Arlodotexe]

We should consider the advantages we'd get building the MarqueeControl on ItemsRepeater instead of manually repositioning two text segments via Storyboard/code-behind. It would require a full rewrite, but in the long term it may be worth it.

@michael-hawker I don't have experience with building a custom layout with ItemsRepeater, so any insight you could add here would be valuable.

Originally posted by @Arlodotexe in #548 (comment)