mp-api for MPDataRetrieval needs upgrade badly

[ardunn]

See here: https://matsci.org/t/403-returned-the-api-key-doesnt-work/51353/7

[AntObi]

Hi, I'm happy to take on this issue.

Do we want MPDataRetrieval to only support the mp-api or do you also want to preserve compatibility with the legacy Materials Project?

It still works with the legacy API, so at least I think any upgrade should ideally be able to interface with both