No support for ctrl key while dropping

[Piotr Jasiun]

In browsers like FF, IE you are able to press ctrl before (and hold it until) dropping a content. This way you should be able to copy dragged content instead of moving it.

1. open sample with CKEditor with new DnD
2. drag any element/text inside the editor
3. while dragging hold the ctrl key
   

Notice how the cursor changes to indicate a copy

4. drop it in any place
5. release ctrl key

Expected result:
Origin instance should not be removed.

Current result:
Origin is being moved ignoring ctrl key.

additional info:

1. Blink does not provide handling for this feature
2. I'm not sure if this feature is present in OSX