Some headers were currently only added to the templates but not to other components (e.g. SabreDAV / JSON / etc...)
The migration to base.php ensures that the headers are served to all requests passing base.php
In some specific situations, the L10N bundle isn't loadable yet (for
example when there is an issue with the app_config table). In such case,
we still want to be able to log the real exception.
This fixes errors that say "OC_L10N_String::__toString must not throw
exceptions"
