application: Add CallsSettings class

This makes it easy to access application wide settings.

src/calls-application.h

@@ -33,6 +33,9 @@ G_BEGIN_DECLS
 
 G_DECLARE_FINAL_TYPE (CallsApplication, calls_application, CALLS, APPLICATION, GtkApplication)
 
-CallsApplication   *calls_application_new    (void);
+CallsApplication   *calls_application_new                               (void);
+gboolean            calls_application_get_use_default_origins_setting   (CallsApplication *self);
+void                calls_application_set_use_default_origins_setting   (CallsApplication *self,
+                                                                         gboolean enabled);
 
 G_END_DECLS