A GtkGestureDrag is used for color selection, removing also the
need to track the pointer state in widget data. The GDK grab performed
just to set the crosshair cursor has been replaced by a call
to gdk_window_set_device_cursor(), which will be unset if the
drag operation is finished, or cancelled due to the implicit grab
being broken.
The propagation phase property/methods in GtkEventController are gone,
This is now set directly on the GtkWidget add/remove controller API,
which has been made private.
The only public bit now are the new functions gtk_gesture_attach() and
gtk_gesture_detach() that will use the private API underneath.
All callers have been updated.
Implement popups in the editor, fix window sizing, fix RTL flipping.
GtkColorPlane is now using adjustments, and GtkColorEditor is using
adjustments as its model as well.
