Integrate anystyle

[koppor]

https://anystyle.io/

This can replace FreeCite or just be an additional button.
See https://help.jabref.org/en/NewEntryFromPlainText for the current UX.

[Siedlerchr]

Refs JabRef#561

[koppor]

This is especially important, because FreeCite was shut down recently:

https://library.brown.edu/libweb/freecite_notice.php

[koppor]

Online web service currently shut down: - https://github.com/inukshuk/anystyle#web-application-and-web-service

[koppor]

Follow up at JabRef#5614. Will be GROBID instead of anystyle

[koppor]

Anystyle is back:

I'm happy to announce that https://t.co/YufeDlCUHj is back online. It has been updated to use the latest version of the parser and the we app itself is now also open source!

— C. Auguste Dupin (@1nukshuk) December 23, 2019

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