Import account which is already present: add warning ?
Currently: Accounts can be imported an unrestricted number of times. They are all considered to be independent devices, so it is expected to work fine.
This is confusing. 99% of users just don't want to have the same account twice on the same machine. For them, it will juste be a bug and bad UX.
What we should probably do: Print an explicit warning when one tries to import an account which is already present.