Don't create drafts every time a component is edited.

TNL-399
@cpennington Is this a legitimate way to see if the xblock really needs to persist changes? 

Also, why is it that we need to support the ability for an xblock to persist changes when the xblock editor is shown (STUDIO_VIEW), but we don't when an xblock is rendered in its student "preview" view within Studio?

@dmitchell and I were talking about this bug fix earlier today, and he was questioning if we really need to call update_item here at all. I know you have felt strongly about this in the past. Can you summarize your arguments?

Thanks!
Christina