Remove "Duplicate" functionality from embeds (if not done already)

[graste]

The "duplicate" buttons on embedded entities can be removed from the markup and the javascript widget(s). The duplicate functionality in the validators for post payload __action should probably be removed as well.

The removal is necessary as the duplication of embeds is not a simple case of duplicating data. The semantics behind the managed data may prevent having that feature. That's why it's better to implement that as a custom feature on projects instead of having it in this boilerplate.