added reporter to send mail when check fails

The idea of the MailReporter cames, when I created a little Symfony Command which will executes the checks. In this case it will be helpful to send a mail when a check fails. So you can easily create a cron job which triggers the command and inform you automatically.
like I said .. I prefer to have a generic parameter here to activate reporters that while enabled are not intended to be always enabled. this logic we could then also add to the controller and we would then have a generic solution.