Fix draggables

Draggables/Droppables needed a bit simplification, Ink-ification and documentation

New features:

 - We're able to use selectors in the "accept" option, thus not being limited to select only a className
 - Constructor now takes a selector string instead of an ID
 - A few preset event handlers, "move", "copy", "revert", to avoid writing functions for those common cases.
 - Changed a few option names while maintaining backwards compatibility.
 - Take data-attributes as options too