Set the properties when updating title and status. In GimpImageWindow,
connect to notifications of the properties to update window title and
statusbar.
...which is connected to the window's active display. Remove updating
the window's menubar_manager from GimpDisplayShell's scaled()
impl. Had to hack around a bit with the new API to set the window's
active display because they are still the same widget.
And add gimp_image_window_set_active_display(). Call the new function
when creating a shell. Will all be done by the means of a GimpContext
later, but is a step to get rid of FIXME hacks.
Also move some of their related code and update other code to
go via gtk_widget_get_toplevel(), but also add some horrid temp
/* FIXME image window */ hacks.
Also remove GimpDisplayShell's "window_state" member. Use
gtk_widget_get_toplvel() to get to the GimpImageWindow when we need a
display shell's fullscreen state.
Create the menubar_manager when the construct property is set, assert
for its presence in constructor(). Pass the newly required construct
property to g_object_new() in gimp_display_shell_new().
