This commit adds LoginAccount endpoint.
This makes it consistent with CreateAccount and RestoreAccount as they
use similar config.
The notable difference with the previous endpoint is the API, which is
the same as CreateAccount/RestoreAccount, and the fact that it will
override your networks configuration.
Storing them in the config is now not needed anymore, as that's always
driven from the backend, and we won't allow custom networks in the new
wallet.
