Allow update smtp settings in admin panel

[DeanMarkTaylor (Dean Taylor)]

This feature request is also relevant to multisite installs as per this support thread:

@suanfazu

how to configure different smtp email settings for different sites?

@sam

We don’t support multiple outgoing SMTP servers in multisite

@5minpause

would consider given a pull request?

@sam

Sure, if you can pull it off, its pretty complicated, but I would be open to have a PR for it and would kind of prefer if email settings were in site settings as long as they can be shadowed by globals.