Fixed EZP-21563: fatal error w/ approval wf + ezoe upload

Fix for https://jira.ez.no/browse/EZP-21563.

When an approval workflow is in place that affects the media section, a fatal error will occur if an editor tries to upload an image/file from eZOE.

This is a regression from https://jira.ez.no/browse/EZP-19660, where a transaction was added to the publish operation; since publishing doesn't end, the transaction stack is invalid, and this is what causes the fatal error.

With this PR, the unapproved embed can be used during edition. If the embedding object is published, the unapproved embed(s) won't appear in content/view, and will start appearing as soon as the embed content is approved.