No feedback to user about running simulations or their ending

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?

issue にはソースファイルやテストが指定されていません。simulate アクション、その実行中タイマーの状態、plots への遷移、app.log メッセージを追跡します。UI が実行中、完了、失敗の状態を明確に区別し、ユーザーに何をすべきか伝えられれば完了です。

索引モデルが issue の本文から書いたものです。