Big additions to Mailbox Alert!

I've added an option to use the internal alert service from mozilla, which shows an alert suited to your system, with the icon you select. You can also specify a sound to be played now. Of course, calling an external tool is still possible.

It should also be a lot more user-friendly now, with browse buttons etc.

I think this is the last major feature addition before 1.0, so any ideas you might have must be really good to get into that ;) I will of course fix any bugs that are left, and have a few things that i will add or try to add in 0.9, the most important ones of those are:

• Internationalization support Replace the built-in english texts with language keys, so other languages can (eventually) be supported.
• Junk mail At the moment, you also get alerts when junk mail arrives, because Thunderbird puts it in the folder before removing it again. I don't know if this can be recognized but it would be nice if this is possible.
• Support for Virtual Folders