color-settings: Fix ColorSettings release
The dialog should not be destroyed, since it is owned by the GtkBuilder,
which is released at the end of main(). Also, when the dialog is
embedded in the setting manager, the wrong connection of
color_settings_dialog_destroy() causes segmentation fault, since the
pointers accessed are not the right ones.
Fixes #211 (closed).
Edited by Gaël Bonithon