Add conversational entity linking into REL

[stefsmeets]

This PR implements converstational entity linking from @hideaki-j into REL.

First I refactored the CREL code (see informagi/conversational-entity-linking-2022#1). I left the code as-is as much as possible, and tried to depend on functions already in REL where possible. Then I copied all the code over into ./src/REL/crel.

I added some tests and documentation for the new CREL functions.

I also refactored the server to use fastapi/pydantic (in #147 so you can see the changes). I then branched this off #147, which makes it much easier to implement the conversational entity linking into the server. Note that the API itself did not change, I just added conversational entity linking to it. Fastapi/pydantic will make it much easier to update the API later on.

To check out the server working, see ./scripts/test_server.py for an example.

Todo

• Align conv EL with REL itself (re-use parts where possible)
• ConvEL has its own mention detection using Bert, this should be aligned with @eriktks work.
  -> Revisit when Mention detection with Bert #151 is merged
• Figure out what the correct API for interacting with the server should be.
• Update documentation (setup, paths etc, how much should this be part of REL?)

Follow-up:

• Refactor bert_md.py once Mention detection with Bert #151 gets merged.
• Update API (see Server architecture #146 (comment))

[stefsmeets]

Hi @chriskamphuis and @hideaki-j I think this PR is pretty much done, could you have a look at it and let me know what you think?

[chriskamphuis]

@hideaki-j Can you look at this, as you created CREL, I am not familiar with it

[hideaki-j]

I have skimmed through the changes of CREL parts, and it seems to be OK (Stef and I had a meeting about this and I have already shared this with him 😉) I will take the time to check the documentation and test etc in detail when I find time but I think it is good to move to the next step for now.

[stefsmeets]

Hi @hideaki-j @chriskamphuis, if you are happy with the changes, don't forget to press the 'Approve changes' button, so that the code can be merged :-)