Inject variables from EmbedToHtml5 converter in proper namespace

See https://jira.ez.no/browse/EZP-20554

This hardly seems like the best solution to this issue, but it does solve it. Someone with a better understanding of the inner thoughts of eZObjectForwarder and $tpl->elementValue may be able to create a better solution. 

Given that this is likely temporary until Twig can properly handle embeds on its own, this may serve as an adequate bridge.