CRM-8559 getNavigationList should return translated labels

When you edit a report in a non-english linguage, the option provided in the 'Parent Menu' select list are not translated.
This is due to the core method getNavigationList which returns non-translated labels.

A solution is provided in the attached patch, it inializes the i18n singleton and ask for translation in the _getNavigationLabel method.
It affects the CRM/Core/BAO/Navigation.php file.