[change] Check if user has notification enabled before prompting to verify email address

[nemesifier]

Follow up of #281 / #336, to be done once we merge the gsoc24-rebased branch in master.

When a user logs in, if he doesn't have any verified email address we say that notifications are enabled and prompt to send the verification email again.

However, we aren't checking if the user really has any email notification enabled.
I think it would make sense to check this as not all users will care about email notifications and prompting them to verify their email address may be annoying for some.

I think we should:

• Provide a method which checks whether the user has any email notification enabled
• Use this method before checking if the user has any verified email in check_email_verification.