CallWindow: add top and right margin to the preview container
CallWindow: add top and right margin to the preview container

So that when it's placed on another corner, it still has some
margin.

https://bugzilla.gnome.org/show_bug.cgi?id=656268

Distrotech/telepathy-account-widgets,GNOME/telepathy-account-widgets,Distrotech/telepathy-account-widgets,GNOME/telepathy-account-widgets,GNOME/telepathy-account-widgets