Use gtk.Widget.set_direction to properly align roster items
Place of text in roster is determined by it direction instead of GUI direction.
If a screen name is in RTL, it will be placed on the right side of contact row.
Note: This is partially "fixed" (nasty and bad hack) in RTL widget of GTK+ 2 and is seem to be fixed, perhaps appropriately, for LTR and RTL widgets of GTK+ 3, so do not apply suggested patch on GTK+ 3 branch, yet, until this matter is verified.
Use gtk.Widget.set_direction to force text placement.