Add predefined email communication functionality

[joseluis]

This would need to be a config option. If an email address is supplied then the credentials are sent there.

I've come across the expectation several times that people assume I will notified immediately of the credentials, and they forget to send an email with the link.

It would be handy for support services.

It may probably be a good idea to display a default message warning about it too. E.g. "A link to this credentials will be automatically sent to such@and.such".

This would be related to #19 but depending not on the user but on the particular server installation.

I'm thinking that an alternative soution could be if this config option would fill the default value of the new email field proposed in #19. It's not the same thing at all but they are not incompatible either. It would be perfect to have both.