Integrate widgets with the new copy/cut/paste dataTransfer

[Piotrek Koszuliński]

Widgets use copybin, while on modern browsers they can now use the dataTransfer integration which we introduced in 4.5.0. The question, though, is whether we have to do this, because on all IEs we'll have to leave the copybin, so we would need to branch the code. There may be a strong argument for this change - recognising content origin (internal, cross editor, external) and filtering Webkit/Blinks awful inline styles.

[Piotrek Koszuliński]

For now we don't see a clear need to make this change. There are some advantages, but at the same time it would increase complexity rather than decrease it. We can do it later when the situation will be clarified by some bug reports.