Schedule: Add the option for Overlay Layouts to be disabled when another Regular event is active

[exalate-issue-sync[bot]]

Maybe you have a bunch of Layouts in rotation, but one of them wants to be full screen video or similar.

In the CMS this would be an option on the Schedule form.

OP: https://community.xibo.org.uk/t/disable-an-overlay-for-certain-layouts/13742