Draggable array elements, drag handle

[AndrewIsh]

It would be useful to have an optional, styleable drag handle for ui-sortable arrays. This would serve as a useful hint to users who may not know that the array is re-orderable.

[Anthropic]

@AndrewIsh can you check if json-schema-form/angular-schema-form-bootstrap#19 solves your issue?

Please re-open if it does not :)