Moves XML serialization for content/media/members to a resusable class: EntityXmlSerializer to remove the circular references we have by using the ToXml extension methods from directly in the services. This has been completed for the ContentService, next is Media and Member services. Updates the ContentService to not perform CUD operations for preview or published xml, this is now done at the repository level and now done in a single transaction for the saving and publishing events. Still need to do that for the member and media services too and the remaining methods in the content service