Define a port for mailer default url option

Our current server is behind an Apache2 ReverseProxy. It listens on port 80 and redirects the requests for the application's port. If we don't define the port on the mailer default url option, devise will generate a link for password confirmation that wont't exist because it will try to access the domain on port 80.

This commit fixes it by adding a default port to the mailer configuration sample and using it to create the default url option.