add Marketplace siteLogo to Persona screen (bug 892719)

https://bugzilla.mozilla.org/show_bug.cgi?id=892719

r? @mattbasta

![](http://f.cl.ly/items/171w3e0P131Z2v2m252t/Screen%20Shot%202013-09-03%20at%204.05.52%20PM.png)