Decorate pasted links so that they look like links
By default, draftjs will represent pasted `<a>` tags as `LINK` entities, but it doesn't do any default decoration of these links. Add a decorator to do so.
Most of this was taken from https://github.com/facebook/draft-js/blob/v0.8.1/examples/link/link.html (note the version, v0.8.1).
