UX for "account logged out" -> "account logged in" transition needs improvement

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### Feature description

When an account is in "logged out" state, there is a UX problem with logging back in. "Log in" button in the account menu doesn't
*immediately* produce a visible response in the app. You can't tell if the application is going through the login sequence slowly, has silently failed (say, due a connection hang up), or if your click didn't register.
This can be important, because in the first case no action is required on user's part, while in the latter two it is, and the user won't get their files synced otherwise. As such, these situations need to be distinguishable.

There are several possible ways to indicate what's going on:

a. the basic steps (establishing HTTPS connection, attempting login, success/failure) can be shown in the event log. Simple, but that would produce log entries every time the device loses connection to the server.
b. visual indicator on the account menu entry to show that the app is currently attempting to log into *this* account. Less log spam, but requires UI changes.
c. visual indicator on the tray icon to show that the app is currently attempting to log into *some* account.

Any combination of those would be welcome.