Mailwatch plugin ported to new panel

[Jasper Huijsmans]

Hi all,

To test the new panel plugin API, I decided to try and port one of the 
more complex plugins, mailwatch. Well, it was a piece of cake ;-)

Whether this is due to the exemplary modular design of mailwatch, or my 
l33t API designing skillz, I'll leave for you to decide ;-)

Anyway, I imported it into branches/experimental of the 
xfce4-mailwatch-plugin in SVN. Brian, I hope you don't mind. Feel free 
to ignore it and come up with something better.

It should just work, but of course I may have missed a couple of things, 
so if you're feeling bored, you could try it out.

	Jasper