Highest account index lookup is sometimes interrupted: add progress/loader

[314159265359879]

When the user restores a wallet the highest account index is determined, this can take a long time when there are a lot of accounts. If the process is interrupted it fails and only the first account of the wallet is displayed.

We should show a progress bar/loader so the user knows to wait whenever they restore a wallet.

Once this pops up in the console, the process is completed:

A loading icon is probably best because you can't know in advance how long it will run for.

[linear]

LEA-2133 Highest account index lookup is sometimes interrupted: add progress/loader

[314159265359879]

@kyranjamie would it be possible to show a loading icon as the wallet looks for accounts with activity to determine the highest account index?

[markmhendrickson]

Even better would be that we continue lookups in the background even if the user closes the window prematurely upon adding a wallet