Unset fullscreen when new client is spawned

[dm1tz]

Current behaviour: spawning new client along with fullscreen window makes this window remain behind newly created one.

current.mp4

Expected behaviour: when the new window is spawned unset the fullscreen client back to tiled.

expected.mp4

[sevz17]

Makes sense, we could also create a dedicated scene tree for fullscreen clients, this way when creating clients they will appear below the fullscreen clients. Or both