With wallet_type=="standard", if the user enters a 2fa electrum seed, the "next" btn is disabled.
This is a regression in the new wizard, the old one used to "redirect" seamlessly.
This commit does not fix this, but at least shows a user-friendly warning message.
Note: would be nice if the wizard redirected automatically, in both directions (2fa->std, std->2fa).
The old wizard implemented std->2fa (probably the more common case hit by users), and had this
warning message shown for the 2fa->std case. Now I am repurposing the warning also for std->2fa.
77c55d78b7