adding the ability to style dragged div

[kjda]

[ir4y]

Hi @kjda Thank you for your work.

Why do you need this feature? Since you can use any render function for dragged element http://package.elm-lang.org/packages/ir4y/elm-dnd/2.0.0/DnD#dragged you can add your styles there. Is it not enough?

As for me this styles https://github.com/ir4y/elm-dnd/blob/master/src/DnD.elm#L302 should be internal and do not need to be overridden.