Added e-mail notifier

Hello,

In issue 618 there was a request to add an e-mail notifier (https://github.com/RuudBurger/CouchPotatoServer/issues/618). The last comment was "If you want this, you can always send me a pull request ;)". This is that pull request :). I also missed the option to let Couch Potato notify me via an e-mail. Thus I created that notifier :).

I've only tested this on the platform I run Couch Potato on, which is Gentoo Linux with Python 2.7, but it works flawlessly there.

If you have any questions, please let me know.

Regards,
Cybertinus