onDropFile

Handles a DropFileEvent. The event happens when a drag&drop file over the window happens.

Events are emitted with the following types:

• DropFileEvent.Type.START - When a drag with a file enters the window (still not drop). This is a good time to highlight that the action will perform a file drop

• DropFileEvent.Type.DROP - When the drop is effectively performed. DropFileEvent.files should be set here.

• DropFileEvent.Type.END - When the drag is cancelled or have been executed already.