Containers can be locked since the model came in, and a locked container keeps
its index while others are inserted, removed or swapped around it; nothing could
lock one. `komorebic toggle-lock` locks the focused container, or unlocks it,
and the `LockMonitorWorkspaceContainer` and `UnlockMonitorWorkspaceContainer`
messages lock and unlock a container by the index of its monitor, its workspace
and itself, for a program such as a status bar.
The vm-commands sweep locks and unlocks a container.
