Handle exceptions when loading named objects, log errors in debug mode

[emodric]

We can use a monolog.logger tag to specify a separate channel, to make it easier to grep through logs, e.g.

netgen.ezplatform_site.twig.runtime.named_object:
    ...
    tags:
        ...
        - { name: monolog.logger, channel: ngsiteapi }

[pspanja]

Thanks @leohajder!