This commit updates the code to use the recently introduced API. The new functions improve the legibility and maintainability of the code, and makes it easier to work on new features. https://bugzilla.gnome.org/show_bug.cgi?id=766922
This avoids the confusion of the name gnome-control-center.c and is consistent with all the other classes/files in the project. https://bugzilla.gnome.org/show_bug.cgi?id=692174