Action identifier for administrative privileges

Add a method that returns the PolicyKit action identifier for modules
that requires administrative privileges.

Issue: #11

src/lib/preferencesmodule.cpp

@@ -39,6 +39,11 @@ namespace Hawaii
         {
             return false;
         }
+
+        QString PreferencesModule::administrativeActionId() const
+        {
+            return QStringLiteral("");
+        }
     }
 }
 

src/lib/preferencesmodule.h

@@ -202,6 +202,15 @@ namespace Hawaii
              * This method returns false by default.
              */
             virtual bool requiresAdministrativePrivileges() const;
+
+            /**
+             * @returns the identifier for the action that requires
+             * administrative privileges.
+             *
+             * If this module doesn't require administrative privileges, this
+             * methods returns an empty string.
+             */
+            virtual QString administrativeActionId() const;
         };
     }
 }