[Fullscreen] App should exit fullscreen on logout

### What
If full screen is active, and the user logs out, the app should exit full screen.

### Why
Current behaviour for non-screen mode is: user logs out, sees the login screen. If the login screen is closed by the user, the app process is still running, and the **login screen can be brought back by clicking the dock icon**.

^ The part described in bold will not work if the app was in full screen before log out:

https://user-images.githubusercontent.com/73365754/110345013-ca90ab00-8036-11eb-956e-ec6ea52772e3.mov

No files or tests are named. Reproduce the issue by entering fullscreen, logging out, closing the login screen, and trying to bring it back from the dock; trace the logout and fullscreen behavior. Done means logout leaves fullscreen and the login screen can be restored from the dock as in non-fullscreen mode.

Written by the indexing model from the issue text.