Allow overlaying dashboards to the gallery photos

[tmigone]

User would like to have content (weather forecast, agenda) in the foreground and photos rotating in the background. https://magicmirror.builders/ might be a good reference.

We probably don't want to implement this directly into dash, but maybe as a webapp that uses dash in the future.

[jellyfish-bot]

[tmigone] This issue has attached support thread https://jel.ly.fish/f29b4b0d-d32d-4255-8f58-56205c44a7eb