No feedback to user about running simulations or their ending

Dieses Issue hat noch niemand übernommen.

I've got a simulation running now. After I clicked "simulate", I think I did get a "running simulation" timer initially, but it seems to have gone now, so I'm back to the screen with the "simulate" button:


There's nothing here to tell me if the simulation has finished (I assume it didn't because the screen changes to the one with plots when that does), or if the simulation has failed. I *think* it's still running---app.log still hasn't got anything after this:

```
2023-07-13 16:38:20,175|root|DEBUG - ComponentSync disconnecting from simConfig.cvode_active
2023-07-13 16:44:14,958|root|INFO - Scheduling simulation on 1 cores with ...
2023-07-13 16:44:14,963|root|DEBUG - Running single core simulation
```

but there's no way to tell. As a user, I don't know what to do---should I wait more, should I click simulate again, should I start again from scratch?

In der Issue werden keine Quelldateien oder Tests genannt. Verfolge die simulate-Aktion, ihren Zustand für den laufenden Timer, den Übergang zu Plots und die app.log-Nachrichten; fertig, wenn die UI die Zustände „läuft“, „abgeschlossen“ und „fehlgeschlagen“ klar unterscheidet und dem Benutzer mitteilt, was zu tun ist.

Vom Indexierungsmodell aus dem Issue-Text verfasst.