Add NEL visualisation (links to entities in a knowledge base)

[shigapov]

Description

Current NER visualiser cannot show links to entities in a knowledge base. This PR adds NEL visualisation using manual=True option in displaCy.

Types of change

This is enhancement, see issue 9129.

Checklist

• I confirm that I have the right to submit this contribution under the project's MIT license.
• I ran the tests, and all new and existing tests passed.
• My changes don't require a change to the documentation, or if they do, I've added all required information.

[svlandeg]

Thanks for the PR, much appreciated! I have some small comments, but I think this looks good in general. I'll also ping Ines to see whether she might want to review, too :-)