Bring back redundant notifications for GtkToggleButton::draw-indicator

Bring back redundant notifications for GtkToggleButton::draw-indicator

GtkCheckButton sets a different initial value for this property without
actually changing the declared default, and then relies on change notification
to update other properties (such as xalign). This, combined with glades
insistance on putting default values into ui files creates a situation
where we can't remove the redundant notification for ::draw-indicator
without causing lots of checkboxes to suddenly have centered labels.
This was seen in gnome-terminal, evolution, and other applications.

Therefore, keep the extra notification for now. This can be revisited
when we clean up the button hierarchy.