craft.js Added events.draggedOver part 2.5

Kodak bot went crazy with #184 and automatically merged the PR. Hopefully this won't be auto merged.

This PR adds draggedOver to the events. It's almost the same as #37 but targets the next branch and the new EventHandlers, which also gives us a cleaner API. (#37 will be obsolete).

Since the new EventHandlers introduced a Set as the store for the EventHandlers, we can now store not only the id of the node we are dragging over, but all of its ancestors, too.

I also updated the Basic example with two different examples on how to make use of the new API.

Closes #28 Closes #37 Closes #183

The only complaint we have with the new API is the name draggedOver. @prevwong suggested to re-use the hovered event. If an element is being hovered, and the dragged event stores at least one nodeId, we are dragging over an element. I prefer a more explicit API over an implicit one. As a counter argument Prev suggested to make use of the EventHelpers.

I, too am not a fan of the name draggedOver but lack the creativity to come up with a better name, but I prefer the DX of having an explicit event for dragging over elements. My argument is, that the developer could discover the API with just using code completion and without having to have a look at the documentation of hovered or looking at a guide / example.

Maybe @matdru, @mresposito or @timc1 can chime in and discus the API. Not only these guys, but everyone is welcome to leave a comment. 👍