#1431 Notify Players of PMs Using Registered Email

[AntumDeluge]

In the past, I have spent extended periods without logging into Stendhal or the website. I hadn't realized that a player had sent me a personal message. It would be helpful, in my opinion, for players that have a registered email, to have the option of being notified of PMs via email. And I suppose the best way to do this would be via Stendhal's web page.

GitHub issue: https://github.com/arianne/stendhal/issues/155