Adding SMTP configuration

[zallaevan]

Email notification of new logins is enabled but only possible using SendGrid credentials. I would suggest adding environment variables to allow sending emails using SMTP servers of our own, if possible. I would work on a PR but my knowledge is not that extensive yet, so I will try to do my best in order to implement it. However, I want to point out this feature to others as I am sure more qualified people will know how to do this.