* Removed invalid options for the sendmail transport that were causing Nodemailer to return the SMTPTransport instead.
* Removed options for rate limiting in admin email interface. Added new option for toggling whether to use pooled connections.
* Fixed typo at emailer.js line 66 (serice -> service)
* When custom SMTP user and password is empty no authentication is attempted
* Added options to choose custom smtp connection security
* Made custom smtp connection security strings translatable
* Changed switch to if-else for custom smtp security option
* Fixed emailer.js lint errors
* Move custom setting to top of list
