Show which layouts are actively being used by the streamer

[Lethalchip]

If a streamer is not forcing a specific layout, it's obvious that the layout showing on stream is the active one. Designated by a ✔ in the layout section.

However, if a streamer does take advantage of the force layout param in the overlay URL (&layout=LAYOUT_NAME), there is no way an editor will know if that layer is in use. Meaning the editor could accidentally modify a "hot" layout without realizing it.

To remedy this, we can add a reducer which the overlay route will fire off that lets clients know what layouts are currently being monitored. We will need to add a column in one of the tables, or make a new table for this. Which is a breaking change.

Requested by @grand__ in discord. Thank you!