Bakery setup wizard for SMTP config + separate SMTP setup in it's own command

[lcharette]

To quote @alexweissman

could do some kind of wizard with Gmail, Mailgun, Other as options. the same way we do for DB setup in Bakery

To help with recurrent SMTP issues (See #552 & #776)

Simply need to add a selection when creating SMTP server :

1) SMTP
2) Gmail
3) Mailgun
4) sendmail
5) No email support / later --> big warning registration won't work

And ask pertinent question when dealing with gmail for example.

To sync with #872.

Also, we should separate setup command into setup:db and setup:smtp

[lcharette]

This was planed for 4.2, but finally been added to hotfix for 4.1.18 release. Requires a composer update.

[alexweissman]

Released in 4.1.18.