Bug 910552 - patch2 - [Settings] Call Barring menu not implemented

2 - Adding Call Barring menu item and dumb screen (no interaction)
The initializing part is not a problem, we could do it as we enter the panel, but we need it loaded for other things, at least if we don't want to duplicate the `visibilitychange` and `panelready` event handlers (both in `call.js`). Also, I tried to use a require only when we need to call the panel, but seems to fail everytime (not sure what I am doing wrong).