Add Mail second factor plugin
See #1629 (closed) for details
New parameters:
mail2fActivation mail2fAuthnLevel mail2fLogo : Same as other 2F modules
mail2fSubject: If left blank, use translation files
mail2fBody: If left blank, use HTML template, $code will be replaced by the generated 2F code
mail2fCodeRegex: Code format for String::Random, defaults to 6 numbers
mail2fTimeout: Allow an admin to set the token timeout, if left blank, formTimeout (120s by default) will be used. Some users may need more time to dig through their email account