New mailgun domain; Opera doesn't own FastMail anylonger

[Opera split from FastMail in 2013](http://blog.fastmail.com/2013/09/25/exciting-news-fastmail-staff-purchase-the-business-from-opera/) so I renamed the provider and dropped the Opera icon to reflect the change. I took FastMail's logo from https://www.fastmail.com/favicon.ico and https://www.fastmail.fm/help/legal/press.html states that:

> If you are writing about FastMail, or integrating FastMail support into your product, we're happy for you to use our logo. Please note though, the FastMail logo must only be used to represent FastMail, not any other product. You must not use our logo in whole or in part for your app's icon.

However, I'm not exactly sure if this this covers the use of their logo in a product like this? I think we also have to review the licenses of all other currently used icons as it might not even be legal to use/ship them with the extension (which would be very inconventient).

I also added `mailgun.info` to the list of Mailgun/Rackspace domains which I have seen in the wild.