Watch the ledger device connection and warn if lost

[monikasmolarek]

Currently, Wallet doesn’t notice when the device is disconnected until the very last step of a device-related process.

The icon indicator also stays green showing the user that the ledger is still correctly connected, while in reality it might be unplugged.

To cover:

• Verify the behavior after the Spacemesh App is closed on the ledger while it's still connected to the lite wallet app.
• Verify the behavior after the ledger is locked (i.e. being idle) while it's still connected to the lite wallet app.
• Verify the behavior after the ledger is unplugged while it's still connected to the lite wallet app.

[brusherru]

We cannot watch for the ledger device status, because it may corrupt interacting with the ledger device.

In details, we may watch for it's status only by calling some commands from time to time. However, Ledger device and it's interaction is synchronous, so if there will be any other command (e.g. some code triggered signing tx, while we're running another command to get a status) — both of them may fail. And even if we may solve this in out app by integrating mutex and some more complicated mechanisms, it still may break the whole UX when User will interact with other apps, having our wallet opened.

The good news, that if device is not connected anymore / locked / or app is closed — Wallet App will show a corresponding popup later when User will interact with it.

So I believe it does not make sense, and therefore I'm closing this issue.
If the indicator confuses User somehow – we may remove it, and keep all "connection" things right at the moment when User trying to interact with Ledger somehow.