Disable "Add" button option on nested_table

[jclemans]

A request keeps coming up to add a nested table to a form page and to disable the ability to add a new object here. Sometimes the nested objects are imported or associated in some other way. Adding a custom table view instead of using the fae nested table works as a workaround, but it would be super handy to just be able to render 'fae/shared/nested_table', add_button: false and move on to other things.

[jclemans]

Fix merged in!