Make EvAnnotationWindow not be a subclass of GtkWindow

Submitted by Jose Aliste @jaliste

Link to original bug (#700292)

Description

Currently EvAnnotationWindow is a GtkWindow. The upside of this is that resizing and moving the window is easy (but the position of the window is not being respected, which is another bug) but Evince looses focus whenever the EvWindow is focused. We could look into making the EvAnnotationWindow another kind of widget, which is then a child of the EvView.