Change port numbers in GUI

[trymeouteh]

Please add setting to change the port numbers for SMTP and the web GUI within the web GUI. After changing the port numbers, it will require you to restart the service for the changes to take effect.

[mjpitz]

This is already possible using the existing configuration options: https://github.com/mailhog/MailHog/blob/master/docs/CONFIG.md

You simply need to change the according bind addr declared port.