Icon in item header gets replaced by fa-arrows when closing/opening

[romaincazier]

Short description of the issue

When using icon-name to add an icon in a repeater item header, it gets replaced by fa-arrows when closing/opening because of InpufieldRepeater.js#L457

Suggestion for a possible fix

Check for the presence of the attibute data-icon and replace accordingly

[ryancramerdesign]

Thanks @romaincazier I've pushed a fix for this