See CLI updates on the station screen

When a station installed a new CLI version, its operator screen closed and reopened with no explanation, which looked like a crash.

• Added a line in the bottom bar of the operator screen while the station downloads a CLI update, with its progress.
• Added an "Installing, restarting…" message right before the station restarts on the new version, then a confirmation once it is back.
• Added a short error message when an update cannot be installed; the station keeps running its current version.