Add a page-mod against marketplace to ease reviewer life.

Thanks @diox, who registered me some test account on marketplace dev server and introduced me to the reviewer UI!

That page-mod adds a button in reviewer UI, to easily register an hosted or packaged app, meant to be reviewed, in the Simulator. I choosed to register the app to the dashboard, as it is simplier to implement that way, but may be we want to bypass the dashboard and only push the app to b2g? I can easily see a reviewer dashboard made of tons of apps being reviewed, whereas he don't really want them to be registered...

@myk What do you think about a page-mod? Do you think this code is meant to be hosted in the simulator or should we make another addon that depends on it? Or do something completely different? Is marketplace the only one website where we would like to integrate with the simulator?