Playtime: Transparently disable "Stop/repeat playback at and of project"

[helgoboss]

Because it might cause odd behavior when playing together with arrangement.

See #1327

Alternatively, display it as a warning in the help panel.

There are also other candidates:

• macOS: General / Advanced UI: Throttle mouse-events: Should probably be enabled, otherwise moving mouse can lead to laggy GUI (but this should definitely be more of a recommendation than a warning)