Write more accurate test for paste and drop

I restructured the tests for events slightly.

The tests fail at the moment. So maybe you merge them in and ignore them for the moment.

There are multiple errors:

* The event object is not an argument of the callback.
* Firing a drop event results in a paste event.

I fire the events twice. Once with happen.js and once with vanilla js to show that not happen.js is the cause of this behaviour. I also tried it with the QUnit 1.12 and the old method, but the result is the same.

The reason why the old tests were not showing the wrong behaviour was that paste did fire twice and so the missing execution of the drop callback was not spotted.