Use proper HTML5 API for all browsers

Chrome, Firefox, Safari, and Chromium all now conform to the same HTML5 Notifications API.  This commit make Salvager use them all in the same way.

Also fixed the URL for the Salvager icon that was causing Kaspersky to freak out.  It was still fetching it from drunkensailor.org.

I've tested both the notification creation and the notification permission requesting on:
- Chromium 33 on Arch Linux
- Firefox 26 on Arch Linux
- Chrome 35 on OSX Mavericks
- Safari 7 on OSX Mavericks
I haven't tested on Windows yet. 

I also haven't tested on older versions of the browsers, but they've each been properly supporting the HTML5 Notification draft spec for a while now, so we should be okay there.

This is a high-priority fix, since it's preventing opponents from joining games for everyone who uses Chrome and who has recently updated to Chrome 35.