Fault-tolerant switch of AI providers

[koppor]

1. I configure OpenAI
2. I start chatting
3. I switch to Hugging Face
4. I continue chatting

Expecation: Either JabRef blocks chatting at step 4 - or it works.

Currently:

[InAnYan]

Hmm, need to think. It's not really a problem with switching AI providers.

It's a problem of sending requests

[InAnYan]

I think we should close this issue, because this is directly related to #118.

And as you can see, in chat history we don't track which AI provider was used. So, those are just plain messages